text:
Where can one find guidance from a teacher next year in 2018?
Where on Earth or online are future retreats or classes for an insight practitioner to get Dhamma guidance and/or guidance through some version of the stages of insight meditation?
Are there teachers who might guide an insight practitioner on a one on one basis, given the right situation?

Best and proper way is to approach and ask personal, after having spend a good time next him and have observed his virtues, Nyom Lowbrown.
It's in dependency of assossiation with admirable friends, that one gaines right view. Of course the condition to meet such is a matter of upanissayapaccayena (strong condition causes) and not possible to buy and demand.
So keep always in mind: Better to Give than to Consume. Having not the right attitude and behaviour, one, like many and most, would just meet poor business in Dhamma and Juwel-thieves of many kinds.
People who are really into Dhamma have neither dates nor calenders, but always open doors for those seeing them and having the condition to enter. For those always right in front and near. Someone demand, consume... no way to meet, enter and learn, or being haunted by spirits when enter without a clean and honest mind.
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]

Sounds like you have some inside information on the subject.

It's not good to seek after something to consume at first place, Nyom @Lowbrow , again. Such an attitude cut one off to be guided to look for oneself inside to gain insight and know valid. This costumer attitude is importand to be abounded at first place and its not so easy but place for vipassana already to practice giving and lowering one self on a gross level.

Ok but that's what a dana based retreat is for isn't it? You expect student's to be this way or that way or already knowing what is what? What's wrong with consuming  The Dhamma of a good teacher and the teacher performing good karma?

Do as you like, Lowbrow. If thinking Dhamma can be gained by trade, try it. As my person does neither have nor desire student, relay on the Buddhas way of teaching and don't listen to my person, but it's free and you can not give any reward back: anupubbi-sikkha A Gradual Training to the giver. See also:

Respect, Confidence and Patient, traders might take money or other reward before or after instead and that might be ok for consumer, yet no success in that way, Nyom @Lowbrow . Dana-based... whats that then cheating, calling deal dana. Nobody who teaches Dhamma takes anything for it or expect, in that way you got already in dept torward liberation.

When I say "trade" I don't think I'm being as literal as you are , IDK.

A teacher says come meditate and the students comes and meditates there's no evil exchanged on a dana basis. There is dana taken only when there is a need. I really wasn't trying to get that deep into it. What do you think of places like "Spirit Rock" that claims the student must pay for the "retreat" but not the teacher?

The oral study system, mukkhapatha, still going on at pa-auk monastery.
By this study system, you can practice every meditation step by step.
The teacher will teach you just a bit per meeting for easily to memorize and to practice.
This monastery may not give you an insight meditation first, because jhana is very important for an advance insight meditation. So, pa auk teacher will teach you jhana, first. After that you will ready for an advance insight meditation.
http://www.paaukforestmonastery.org/rules.htm


text:
Did Buddha ever get sick or injured?
Specifically in his last life, both before enlightenment and after.

At least:
Before an enlightenment:

bodhisatta make himself suffering by dukkarakiriyā-practicing,
attakilamathānuyoga, in Mahāsaccaka-sutta.

Aggivessana, it occurred to me, what if I pressed the upper jaw on the
  lower jaw, with the tongue pressing on the palate pushed out, expelled
  and burnt up thoughts in my mind. Then even while sweat was dripping
  from my armpits, I pressed the upper jaw on the lower jaw, with the
  tongue pressing on the palate pushed out, expelled and burnt up
  thoughts in my mind...etc.

It is a very long with many suffering, please, look inside the link by yourself.
After an enlightenment:

One sick,  some physical body suffering, found in
cīvara-khandhaka of vinaya-pitaka.

[135] Tena  kho  pana  samayena  bhagavato  kāyo  dosābhisanno hoti.
Next, the cause is when  buddha's body accumulating waste product.

Two more sicks found in D.N. Mahāparinibbāna-sutta, illness, and
hematemesis.

But when the Blessed One had entered upon the rainy season, there arose in him a severe illness, and sharp and deadly pains came upon him. And the Blessed One endured them mindfully, clearly comprehending and unperturbed.
  ...
And soon after the Blessed One had eaten the meal provided by Cunda the metalworker, a dire sickness fell upon him, even hematemesis (lohitapakkhandikā), and he suffered sharp and deadly pains. But the Blessed One endured them mindfully, clearly comprehending and unperturbed.

Another, injure found in Vinaya Saṅghabhedakhandhaka.

Tato   papaṭikā   uppatitvā   bhagavato   pāde   ruhiraṃ   uppādesi .
Because of broken pieces of big rocks, blood bleed out at buddha's foot.

The conclusion appears in K.N. Apadāna, too. From here, buddha said foot-ache and headache, too. This is a long quote, please see inside the link by yourself.

All of those links lead to huge bodies of text. Can you quote the relevant parts in the answer?

@Euphorbium done.

Are some of those quotes in pali? I do not understand.

I recently translated all of them, except the last longest from apadāna.

The idea that the Buddha had past lives is both a misinterpretation of the term 'pubbe nivasa' in the texts and a later doctrine manufactured in Buddhism (such as the Jataka Tales or Fables). The term 'pubbe nivasa' is unambiguously explained in SN 22.79 and refers to each time in the past the mind clung to one or more of the five aggregates as 'self' (i.e., 'past acquisitions').
As for getting sick & injured, this occurred to the Buddha.
In his 1st noble truth, the Buddha summarised all suffering as attachment to the five aggregates, i.e., attaching to the five aggregates as 'self'.
The idea that "sickness is suffering" is a misunderstanding of the teachings. Ordinarily, i.e., when unenlightened, sickness is suffering because it is a unpleasant experience that is a attached to. But when the physical pain of sickness is not attached to as "self", it is not suffering.
Therefore, the Buddha was free from all suffering from when he attained enlightenment at 35 years old until the termination of life at 80 years old.
For example, the scriptures say:

When the Blessed One had entered upon the rainy season, there arose in him a severe illness, and sharp and deadly pains came upon
  him. And the Blessed One endured them mindfully, clearly comprehending
  and unperturbed.
Maha-parinibbana Sutta: Last Days of the Buddha

There is no extreme wrong in the message, so the upvotes seems to be merely based on bias and aversion, some would say effects of kamma, if being touched.

+1. Yeah. What is up, people? Why all the down votes? "That differs from my opinion" is not a valid reason for a down vote.

To the instances cited by the other two answers, I shall add one mentioned in the Bojjhanga Sutta (chanted as a protection - paritta very frequently). This one is definitely after enlightenment.

Ekadā dhammarājāpi gelaññenābhipīlito, cundattherena tam̐yeva
  bhaṇāpetvāna sādaram̐, sammoditvāna ābhāda, tamhā vuṭṭhāsi ṭhānaso...

Translation: and on one one occasion,  even the Buddha himself, oppressed by sickness, had the Ven. Cunda chant the paritta respectfully to him. Having delighted in it, he then came out of his sickness...
Although the details of this particular instance are not stated, it seems to me, a different one from the other instances mentioned in this thread because such chanting is not mentioned in the other instances. Also please note that the Ven. Cunda is different from the Cunda who served the Buddha his last meal.

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text:
What are the strengths and weaknesses of attempts to describe Nirvana in scripture?
How can we evaluate which description of nirvana is accurate? Also what problems does King Millinda point out about nirvana in his 80th dilemma?

The Buddha himself did not. "Whatever phenomena arise from cause:
their cause
& their cessation.
Such is the teaching of the Tathāgata,
the Great Contemplative." MvI, no "is"'s

@SamanaJohann What about "the sorrowless state", and "the Deathless", and "Unbinding", etc.? Are these not attempts to describe Nirvana, and isn't the word "Nirvana" itself a description?

Hari, is this meant to be a general question about any/all attempts to describe? Or if you're asking about specific descriptions, which descriptions?

Hari might ask for the problem to discripe tast of chocolate for one never tried it and the danger of relaying on something known. Therfore Nibbana is merely found pointed out by description of what it is not and Nibbana is not realy a suitable meditation object for one not having seen by him/her self, out of those reasons. This might be the heart wood of the question, but could be of course meant otherwise. Nyom Hari might know. Baka and Mara tried to convince others with similar attempt. Baka unkownly, while Mara ...

The Pali suttas provide accurate descriptions of Nirvana, such as the 'destruction of craving' (Dhammapada 154; MN 37); 'visible here-&-now destruction of greed, hatred & delusion' (AN 3.55; SN 45.7); 'supreme happiness' (Dhammapada 203); and 'Simile of the Ocean'.
Therefore, the description by Nâgasena given to King Millinda in his 80th dilemma should be compared to the Pali suttas to test its accuracy.
That Nagasena offered a very lengthy answer shows he did not really have a "dilemma" & spoke falsely, when he said: 'Nirvâna, O king, has nothing similar to it. By no metaphor, or explanation, or reason, or argument can its form, or figure, or duration, or measure be made clear.'
These links might help: Nibbana For Everyone & Bhikkhu Pesala What Is Nibbāna?
Have you bothered to read the text or are you a university student looking for an easy answer?

'O happy word, Nâgasena! Speak then, quickly, that I may have an
  explanation of even one point in the characteristics of Nirvâna.
  Appease the fever of my heart. Allay it by the cool sweet breezes of
  your words!'
'There is one quality of the lotus, O king, inherent in Nirvâna, and
  two qualities of water, and three of medicine, and four of the ocean,
  and five of food, and ten of space, and three of the wish-conferring
  gem, and three of red sandal wood, and three of the froth of ghee, and
  five of a mountain peak.'

'Venerable Nâgasena, that one quality of the lotus which you said was inherent in Nirvâna,--which is that?'

'As the lotus, O king, is untarnished by the water 3, so is Nirvâna
  untarnished by any evil dispositions. This is the one quality of the
  lotus inherent in Nirvâna.'

'Venerable Nâgasena, those two qualities of water which you said were inherent in Nirvâna,--which are they?'

'As water, O king, is cool and assuages heat, so also is Nirvâna
  cool, and assuages the fever arising from all evil dispositions.
  This is the first quality of water inherent in Nirvâna. And again, O
  king, as water allays the thirst of men and beasts when they are
  exhausted and anxious, craving for drink, and tormented by thirst, so
  does Nirvâna allay the thirst of the craving after lusts, the
  craving after future life, and the craving after worldly prosperity
  . This is the second quality of water inherent in Nirvâna.'

'Venerable Nâgasena, those three qualities of medicine, which you said were inherent in Nirvâna,--which are they?'

'As medicine, O king, is the refuge of beings tormented by poison, so
  is Nirvâna the refuge of beings tormented with the poison of evil
  dispositions. This is the first quality of medicine inherent in
  Nirvâna. And again, O king, as medicine puts an end to diseases, so
  does Nirvâna put an end to griefs. This is the second quality of
  medicine inherent in Nirvâna. And again, O king, as medicine is
  ambrosia, so also is Nirvâna ambrosia. This is the third quality
  of medicine inherent in Nirvâna.'

'Venerable Nâgasena, those four qualities of the ocean which you said were inherent in Nirvâna,--which are they?'

'As the ocean, O king, is free from (empty of) corpses, so also is
  Nirvâna free from (empty of) the dead bodies of all evil
  dispositions. This, O king, is the first quality of the ocean
  inherent in Nirvâna. And again, O king, as the ocean is mighty and
  boundless, and fills not with all the rivers that flow in to it; so is
  Nirvâna mighty and boundless, and fills not with all beings (who
  enter in to it). This is the second quality of the ocean inherent in
  Nirvâna. And again, O king, as the ocean is the abode of mighty
  creatures, so is Nirvâna the abode of great men--Arahats, in whom the
  Great Evils and all stains have been destroyed, endowed with
  power, masters of themselves. This is the third quality of the ocean
  inherent in Nirvâna. And again, O king, as the ocean is all in
  blossom, as it were, with the innumerable and various and fine flowers
  of the ripple of its waves, so is Nirvâna all in blossom, as it were,
  with the innumerable and various and fine flowers of purity, of
  knowledge, and of emancipation. This is the fourth quality of the
  ocean inherent in Nirvâna.'

'Venerable Nâgasena, those five qualities of food which you said were inherent in Nirvâna,--which are they?'

'As food, O king, is the support of the life of all beings, so is
  Nirvâna, when it has been realised, the support of life, for it
  puts an end to old age and death. This is the first quality of food
  inherent in Nirvâna. And again, O king, as food increases the strength
  of all beings, so does Nirvâna, when it has been realised, increase
  the power of Iddhi of all beings. This is the second quality of food
  inherent in Nirvâna. And again, O king, as food is the source of the
  beauty of all beings, so is Nirvâna, when it has been realised, the
  source to all beings of the beauty of holiness. This is the third
  quality of food inherent in Nirvâna. And again, O king, as food puts
  a stop to suffering in all beings, so does Nirvâna, when it has been
  realised, put a stop in all beings to the suffering arising from every
  evil disposition. This is the fourth quality of food inherent in
  Nirvâna. And again, O king, as food overcomes in all beings the
  weakness of hunger, so does Nirvâna, when it has been realised,
  overcome in all beings the weakness which arises from hunger and every sort of pain. This is the fifth quality of food inherent in
  Nirvâna.'

'Venerable Nâgasena, those ten qualities of space which you said were inherent in Nirvâna,--which are they?'

'As space, O king, neither is born nor grows old, neither dies nor
  passes away nor is reborn, as it is incompressible, cannot be
  carried off by thieves, rests on nothing, is the sphere in which birds
  fly, is unobstructed, and is infinite; so, O king, Nirvâna is not
  born, neither does it grow old, it dies not, it passes not away, it
  has no rebirth, it is unconquerable, thieves carry it not off, it
  is not attached to anything , it is the sphere in which Arahats
  move, nothing can obstruct it, and it is infinite. These are the ten
  qualities of space inherent in Nirvâna.'

'Venerable Nâgasena, those three qualities of the wish-conferring gem which you said were inherent in Nirvâna,--which are they?'

'As the wishing-gem, O king, satisfies every desire, so also does
  Nirvâna. This is the first quality of the wishing-gem inherent in
  Nirvâna. And again, O king, as the wishing-gem causes delight, so
  also does Nirvâna. This is the second quality of the wishing-gem
  inherent in Nirvâna. And again, O king, as the wishing-gem is full
  of lustre, so also is Nirvâna. This is the third quality of the
  wishing-gem inherent in Nirvâna.'

'Venerable Nâgasena, those three qualities of red sandal wood which you said were inherent in Nirvâna,--which are they?' 'As red
  sandal wood, O king, is hard to get, so is Nirvâna hard to attain to.
  This is the first quality of red sandal wood inherent in Nirvâna. And
  again, O king, as red sandal wood is unequalled in the beauty of its
  perfume, so is Nirvâna. This is the second quality of red sandal wood
  inherent in Nirvâna. And again, O king, as red sandal wood is praised
  by all the good, so is Nirvâna praised by all the Noble Ones. This is
  the third quality of red sandal wood inherent in Nirvâna.'
[322] 'Venerable Nâgasena, those three qualities of the skimmings of ghee 1 which you said were inherent in Nirvâna,--which are they?'

'As ghee is beautiful in colour, O king, so also is Nirvâna
  beautiful in righteousness. This is the first quality of the ghee inherent in Nirvâna. And again, O king, as ghee has a pleasant
  perfume, so also has Nirvâna the pleasant perfume of righteousness.
  This is the second quality of ghee inherent in Nirvâna. And again, O
  king, as ghee has a pleasant taste, so also has Nirvâna. This is
  the third quality of ghee inherent in Nirvâna.'

'Venerable Nâgasena, those five qualities of a mountain peak which you said were inherent in Nirvâna,--which are they?'

'As a mountain peak is very lofty, so also is Nirvâna very
  exalted. This is the first quality of a mountain peak inherent in
  Nirvâna. And again, O king, as a mountain peak is immoveable, so
  also is Nirvâna. This is the second quality of a mountain peak
  inherent in Nirvâna. And again, O king, as a mountain peak is
  inaccessible, so also is Nirvâna inaccessible to all evil
  dispositions. This is the third quality of a mountain peak inherent
  in Nirvâna. And again, O king, as a mountain peak is a place where no
  plants can grow, so also is Nirvâna a condition in which no evil
  dispositions can grow. This is the fourth quality of a mountain peak
  inherent in Nirvâna. And again, O king, as a mountain peak is free
  alike from desire to please and from resentment, so also is Nirvâna.
  This is the fifth quality of a mountain peak inherent in Nirvâna.'
'Very good, Nâgasena! That is so, and I accept it as you say.'

If you are a beginner student to Buddhism, what is important to understand is the words 'birth' & 'death' mean conceiving the thoughts: "I am born" & "I will die", as described in MN 140. Therefore, in Nibbana, there is no birth & no death because there is no view of "I am" or "self".

The tides of conceiving do not sweep over one who stands upon these
  foundations, and when the tides of conceiving no longer sweep over him
  he is called a sage at peace.’ So it was said. And with reference to
  what was this said?
“Bhikkhu, ‘I am’ is a conceiving; ‘I am this’ is a conceiving; ‘I
  shall be’ is a conceiving; ‘I shall not be’ is a conceiving; ‘I shall
  be possessed of form’ is a conceiving; ‘I shall be formless’ is a
  conceiving; ‘I shall be percipient’ is a conceiving; ‘I shall be
  non-percipient’ is a conceiving; ‘I shall be
  neither-percipient-nor-non-percipient’ is a conceiving. Conceiving is
  a disease, conceiving is a tumour, conceiving is a dart. By overcoming
  all conceivings, bhikkhu, one is called a sage at peace. And the sage
  at peace is not born, does not age, does not die; he is not shaken and
  does not yearn. For there is nothing present in him by which he might
  be born. Not being born, how could he age? Not ageing, how could he
  die? Not dying, how could he be shaken? Not being shaken, why should
  he yearn?
MN 140

What it is
I guess a problem with the kinds of descriptions in the Milinda Pañha is that, so far as I know, Nirvana is a not-thing -- for example an absence of craving and attachment, and unconditioned (not a caused thing).
What it isn't
If there's a feeling of spaciousness or limitlessness associated with an absence of form/contraint, that (limitlessness) might remind you of an ocean; however, saying that it's like an ocean implies that (like an ocean) it is substantial.
So I'd start by saying it's not like any "thing", no thing which has a form.
Saying it's "like something" is a weak description because you're likely to want to seize that thing, to examine its form etc.
Why it's described in both ways
But as well as being described using negative attributes (e.g. "deathless"), it's also described using positives.
For example it is also described as "an Island" and so on ... I guess the "strength" of that description is that it would be "weak", misleading, unattractive, perhaps incomprehensible to only describe it as "non-existent" ... so it's described in terms of its effect rather than its form (it provides the same effect as an island, i.e. like a rescue from a flood).

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text:
Regarding mindfulness during practice
On personal  practice now no likes or dislike on thoughts  no thinking too. what is the stage of mindfulness?

This stage is basic but proper mindfulness, which is to be constantly maintained. The suttas say:

...that bhikkhu is considered one who lives constantly
  contemplating... strives to burn up defilements, comprehends readily
  and is mindful in order to abandon all liking and disliking toward
  the world.
Anapanasati Sutta

This stage is vicikicchā with uddhacca (doubt and indecision), it is not mindfulness.
Most of buddhist meditations can practiced by thinking of meditation's clear object. Except the eighth jhāna, nevasaññānāsaññāyatana-jhāna, because this jhāna has the strongest mind's power to focus on unclear object. But just object is unclear, the thinking of practitioner still clearly appear.
To resolve this problem, doubt and indecision, you must decide "I forgot my meditation object", then move your focus on meditation object, again. For the example, if you meditating ānāpānassati, go back to focus your breath.

To come to the question raised: So sati means remember, keep in mind and naturally involves thinking, even "like" and "dislike", e.g. judgement? It that right and propably good to add?


text:
Might be possible to gain highest bliss without a loyal relationship?
Marriage (and/or a binding relationship) is not very popular among modern people, who believe strongly in promoted "pseudo-liberality".

As an aside:

The word religion has very similar meaning like marriage, deriving from "religiō".

The classical explanation of the word, traced to Cicero himself, derives it from re- (again) + lego in the sense of "choose", "go over again" or "consider carefully". Modern scholars such as Tom Harpur and Joseph Campbell favor the derivation from ligo "bind, connect", probably from a prefixed re-ligare, i.e. re- (again) + ligare or "to reconnect," which was made prominent by St. Augustine, following the interpretation of Lactantius.

A certain text from a possibly well-known song came to mind the last days:

Love and marriage, love and marriage
  go together like a horse and carriage
  this I tell you brother
  you can't have one without the other.

Next to the possibly well-known wordily marriage issues, the "marriage" stance with the Jewels, for Nibbana in a guided, related way, goes "informal" like that:

“I go to the Blessed One for refuge, and the Dhamma and the Saṅgha of monks.
“May the Blessed One remember me as a lay follower who has gone for refuge from this day forward, for life.

What do you think, or what would you like to share on Dhamma, in relation to bonding, duties in relation to one partner (for worldly bliss), but also in regard of the relation with the Triple Gems for an end of suffering:

Is it possible to gain, either this in this world, or that beyond, if there is no real refuge and total acceptance of the duties in this "contract"?
Can a Hallodri (lightheaded man/woman) expect to gain one or the other, e.g. without real relationship (refuge), if they're either not giving promises or if they're carelessly breaking promises?
And what about relationships where both people mutually agree not to be loyal: can any higher attainment be expected then?

[Note: This is a gift of Dhamma, not meant for commercial purpose or other low wordily gains my means of trade and exchange]

For whosoever, Ambaṭṭha, are in bondage to the notions of birth or of lineage, or to the pride of social position, or of connection by marriage, they are far from the best wisdom and righteousness. It is only by having got rid of all such bondage that one can realise for himself that supreme perfection in wisdom and in conduct.

“Bhikkhus, I shall show you how the Dhamma is similar to a raft, being for the purpose of crossing over, not for the purpose of grasping. Listen and attend closely to what I shall say.”—“Yes, venerable sir,” the bhikkhus replied. The Blessed One said this:
“Bhikkhus, suppose a man in the course of a journey saw a great expanse of water, whose near shore was dangerous and fearful and whose further shore was safe and free from fear, but there was no ferryboat or bridge for going to the far shore. Then he thought: ‘There is this great expanse of water, whose near shore is dangerous and fearful and whose further shore is safe and free from fear, but there is no ferryboat or bridge for going to the far shore. Suppose I collect grass, twigs, branches, and leaves and bind them together into a raft, and supported by the raft and making an effort with my hands and feet, I got safely across to the far shore.’ And then the man collected grass, twigs, branches, and leaves and bound them together into a raft, and supported by the raft and making an effort with his hands and feet, he got safely across to the far shore. Then, when he had got across and had arrived at the far shore, he might think thus: ‘This raft has been very helpful to me, since supported by it and making an effort with my hands and feet, I got safely across to the far shore. Suppose I were to hoist it on my head or load it on my shoulder, and then go wherever I want.’ Now, bhikkhus, what do you think? By doing so, would that man be doing what should be done with that raft?”
“No, venerable sir.”
“By doing what would that man be doing what should be done with that raft? Here, bhikkhus, when that man got across and had arrived at the far shore, he might think thus: ‘This raft has been very helpful to me, since supported by it and making an effort with my hands and feet, I got safely across to the far shore. Suppose I were to haul it onto the dry land or set it adrift in the water, and then go wherever I want.’ Now, bhikkhus, it is by so doing that that man would be doing what should be done with that raft. So I have shown you how the Dhamma is similar to a raft, being for the purpose of crossing over, not for the purpose of grasping.
“Bhikkhus, when you know the Dhamma to be similar to a raft, you should abandon even the teachings, how much more so things contrary to the teachings.

Like always abandoning the raft in the middle of the ocean and not listen/read carefully on what wise say but relay on own ideas., "Buddha" Andrei and your "sodom and gomorrah" approaches. seufz And do not steal by not linking! It might be not given.

https://rationalwiki.org/wiki/Don%27t_feed_the_Troll


text:
Personal practice regarding stream entry
Have experience when notting  the thoughts  as impermanence disappears the body and thoughts  together  .But still  there's somebody looking at and it goes into a  cloudy space. What is this experience?Is it stream winner?

Into the Stream - A Study Guide on the First Stage of Awakening might help to gain what is said to be "Sole dominion over the earth,
going to heaven,
lordship over all worlds:
the fruit of stream-entry
excels them." Much success!

No one can tell if you are, or not a stream enter-er but yourself.  Buddha even gave tools if you wish to proclaim yourself one.   Buddha gave about 60 or so definitions for stream enterer.  From my observation of sutta, stream enterer can be achieved thru one of 5 majors groups;

views + conducts
views + advancement of mind (wisdom or meditation)
views + letting go of 3 fetters
views + advancement of mind + coducts
Views only

(IMO) Almost like one can clime corperate ladder to be come a CEO thu different depts such as from Engineering, Finance, accounting etc..  But one your are in high level, rout options get narrower (none returners are pretty much about views + letting go of fetters)
Some interesting facts about stream enter:

Unshakeable confidence in 3 gems (Buddha, Dhamma, and Sangha) + keeping 5 precepts are the most spoken quality of stream enterer.
Aññā-Kondañña was the only stream-enterer who had only confidence in 2 out of 3 gems + views.  He became a stream enterer (anna means eyes, seeing, sights etc.  another name for stream enter-er) after Buddha finished his first sermon and there was no Sangha right at that time.  Sangha came right after that when Buddha ordained 5 ascetics.  (Aññā-Kondañña became an arahat a few days later at the end of second sermon.)
Those who let go of first 3 fetters are also called stream-enterers.  Interestingly, confidence in Buddha and Dhamma is indirectly put into number 2 instead of first and foremost quality when you use fetters to proclaim stream enterer.   A direct view would be, letting go of doubt in Buddha and Dhamma.
For men (women) in carpenter village, Buddha explained stream-enterer as those with confidence in 3 gems + generosity (without greed which defiles heart, letting of gifts, open handed, taking pleasure in giving etc..  No 5 precepts was mentioned to them.
Practicing in 8 folds path. Another interesting one.  When Buddha asked ven Sarriputta about which of those who sat in front of them were stream enterers, he said those who practice 8 folds path. Tho faith or confidence in 3 gems were not mentioned by ven Sariputta, but in another sutta, those who "sit near and listen" is a characteristic of those who have faith.  so stream enterers have confidence in 3 gems + walk the 8 folds paths.
Confidence in 3 gems + understanding of dependent origination (or 5 skandhas, or 6 sense gates) or understand the raise and fall.
confidence in 3 gems + understanding of 5 sensual pleasures (causal, inability to sustain, deliciousness of it, drawbacks, and nisarana-method to get away from it.)
Views only.  those who only believes that 5 skandhas or 6 sense gates are not permanents, thorn, boils, nest of diseases etc.,  have stepped out of ordinary person and into a noble one.  in mid-flight of entering a stream enter if you will.  Buddha guaranteed he would not die until realize stream entry.
There is correlation between 5 precepts and confidence in 3 gems.  As if someone whom you believe told you the well is poisoned, you automatically stop drinking for it without being told.
maybe more definition which I have missed.  Please let me know.

Bottom line, (IMO) i think stream enterer has spectrum which Buddha tried to explained it in different lights but as I study further of other stages of enlightment such as once or none-returner, seems like the only option is lettering of fetter to make an advancement.

Stream-winning is experiencing the absence of self is peaceful & liberating, which also results in unshakable faith (trust) in the teachings.

It could be access concentration or first jhana.  In that case, good job!  Remember not to yearn for it when you next meditate.  Just do what you've been doing.
On the other hand, you say the space was "cloudy" which means that you could still be struggling with subtle dullness.  Make sure your awareness is still intact throughout the meditation.


text:
How can the concept of Anicca be linked to Sunyata?
Sunyata is more commonly used to explain Anatta, but how about Anicca?

See anattalakkhaṇasutta, anicca and dukkha are fully used to describe anatta, suññata.

“Monks, are feelings permanent or impermanent?”

“Venerable sir, they are impermanent.”
“Those which are impermanent, are they unpleasant or pleasant?”
“Venerable sir, they are unpleasant.”
“Those which are impermanent, unpleasant, changing, are they suitable
  to be reflected, ‘They are mine, I am there, they are my self?’”
“That is not so, venerable sir”

For the example explanation "If something is atta (autocrat, controllable), sāra (real core, like wood core), asuññata (real existent forever)":

It must can control itself to live permanent,
It must can control suffering to be far away from itself forever,
It must can live at the same time/same place/same status forever
(real core must be permanent stable, real asuññata must never
disappear anyway), etc.

However, the fact is nothing can act like that. Every aggregate arising and vanishing depending (paṭiccasamuppānna, saṅkhata) on many variant causes (paṭiccasamuppada), so they are impermanant, and unpleasant. And by that no ability to control anything even itself, therefore aggregate is anatta.
Even nibbāna can not control anything, too. So nibbāna is anattā, also. But it is not anicca and not dukkha, because nibbāna not depending on any causes (asaṅkhata). So, nibbāna is not anicca and not dukkha, too.

Very simple. Anicca is Shunyata's dynamic aspect, while Anatta is Shunyata's static aspect.
Meaning, at a point in time, all entities are essenceless, without a core, without strict boundaries, they are designated/deliniated (=given identity) by conceptual imputation. This is Anatta.
While from the process perspective, entities are transitory collections (aka ephemeral assemblies) of causes and conditions that come together and go apart, in a continuous process of transformation. Like cloud figures that morph continuously and are snapshot-captured as entities by the imputing mind. This is Anicca.
Both of these are simplified reificationistic analogies, what they miss is how much of the designation/imputation/assembly process depends on the mind selectively picking some elements but not others to assemble an entity. Shunyata is deep, very deep.

So to summarise, Anicca is the constant changing nature of entities which is why they don't have an essence in themselves and this means they're devoid of a permanent existence??

Well, not just devoid of permanent existence - devoid of any substantial existence; in actuality there are no entities, they are point-in-time simplifications/approximations with labels stamped on top

If searching for link you may want to read: The Concept of Emptiness in Pali Literature.

This Study on Sunnata (Skt. Sunyata) is mainly based on the Pali text. However, is is known that suyata came into prominence only with the rise of Madhyamaka philosophy of Acarya Nagarjuna. Therfore, no study of Sunnata is complete, without any reference to Sunyata as presented in Madhyamaka philosophy...

It's probably worthy to note here again that suññata has "levels" and someone dwelling in suññata it is not anicca, still produced, in the sphere of more or lesser conductive bhava for release. Sutta and note might be of help: Maha-suññata Sutta: The Greater Discourse on Emptiness. Also "First things first has good advices to go not astray in wrong practice and to get the link right:

If you were to ask people familiar with Buddhism to identify its two most important wisdom teachings, they’d probably say emptiness and the four noble truths. If you were to ask them further which of the two teachings was more fundamental, they might hesitate, but most of them would probably put emptiness first, on the grounds that the four noble truths deal with a mental problem, while emptiness describes the way things in general are.
It wasn’t always this way. The Buddha himself gave more importance to the four noble truths, and it’s important to understand why...

To fall not in Bakas, better Maras trap and into what is called Mohayana rather than Maha.

..."'So, monk, I tell you this: Please, good sir, be effortless. Abide committed to a pleasant abiding in the here-&-now — for it is skillful, good sir, that this not be taught. Don't instruct others.'
"When this was said, I told Mara the Evil One, 'I know you, Evil One. Don't assume, "He doesn't know me." You are Mara, Evil One....

[Note: This is a gift of Dhamma, not meant for commercial purpose or other low wordily gains my means of trade and exchange]


text:
Saving the stink bug
Real question (this happened today). Imagine you're meditating by the fireplace. Outside is cold winter with snow. You have achieved a nice level of concentration, and suddenly you see a stink bug awoken by the heat, crawling into the fireplace. Your choices:

Let it keep crawling into fire, noting "crawling, crawling".
Pray for it to achieve a speedy human rebirth.
"Save" it by taking outside and letting die from the cold.
Put it in a safe place inside the house and let it die from hunger and dehydration.
Put it in a safe place inside the house and provide care and feeding.
Hop on an airplane and take it to China, its natural habitat.
Focus on achieving Enlightenment for the sake of all sentient beings.
Simply switch attention away from the issue.
There is no stink bug.
Mu.
Your own option.

You have about five minutes left on the timer, so you can either finish your meditation properly and then act, or choose to interrupt the session.
What teachings are relevant in this case? What should I do, according to Dharma, and why?

Are you doing intolerant practice ? This might help.

I often wonder about your second point. I wonder if “mercy killing” will allow the bug to be better in another life.

How do you know the stink bug was going to go die in the flames?  Maybe he just wanted to roast marshmallows!

@xxxx how do u know that's a he?? there's a gecko sneaking at the back of the kettle today, said only for getting warm in winter ~ if i heard the silence correctly ~

It is a good oportunity to observe nama constituents feeling, perception, intention, contact and attention.

The moment your awareness was drawn to the reality of a living being about to experience dukkha dukkhata, the most karma neutral action you could do is to take it away from its apparent predicament and go about finishing your meditation without allowing any after thoughts about this past event.

Let it keep crawling into fire, noting "crawling, crawling".

This is wrong meditation. It should be seeing, seeing, seeing..
One can practice Metta, Karuna, Uppekkha or Satipattana meditations or do physical acts of Metta and Karuna. It is not the appearance of the act that determines if your actions are skillful. It is the state of your mind when you perform the action. Whether it is tainted by greed, aversion and ignorance.

I don't remember that the Buddha made efforts to keep people (or animals) from dying, i.e. to preserve (alive) their physical forms. I think he was more focused on teaching dhamma.
The (Buddha's) Vinaya however does include a lot of rules intended to avoid accidental harm (e.g. "don't dig the soil", e.g. "filter water before drinking it") so if you/they are not going to help, at least be careful not to hurt. Perhaps you feel some responsibility (for the bug's welfare) if you may have accidentally brought the bug in with the firewood -- perhaps that's something to be more careful about, next time you pick up wood.
The Jataka tales include a lot of examples of the Boddhisattva caring for beings' physical well-being (including e.g. feeding the tigress), so although "saving" the stink bug might seem out of character for the Buddha, perhaps it is not out of character for the Boddhisattva.
The notion that the bug will die eventually anyway may be true but perhaps a little odd: because isn't that true for everyone, yet not a great reason to do nothing for anyone?
I too use a kind of "barrier" thinking about the house: inside the house is insect-free; outside the house, insects live their own lives without my interfering. It can be considered "compassionate" to keep or put insects outside, because inside is a hostile (e.g. foodless) environment for them. Your outdoor climate is probably more hostile (cold, icy) than mine is now, though.
I think I expect a bit of intelligence in an animal, even an insect. I might hope (though mistakenly) that it would feel the increasing heat and of its own accord avoid getting too close to the fire. If not, the doctrine of equanimity suggests it's heir to its own karma.
Far be it from me to tell you how and when to practice (meditation) but your reluctance to help may have root in some attachment ("You have achieved a nice level of concentration ... You have about five minutes left on the timer, so you can either finish your meditation properly..."). Some stories (e.g. Tetsugen Doko publishing the sutras) suggest some "masters" are willing to interrupt or postpone their (spiritual) ambition[s] in the midst of a mundane emergency which they can alleviate.
Sometimes you can find an answer by putting yourself in someone else's shoes (or by putting someone else in your shoes). "What would Jesus do?" became a popular question or catchphrase among American Christians, for example. Similarly perhaps you might ask, "What would my teacher do? What would my spiritual friend do?". Maybe you mentioned something like that, once, in your answer describing the simplest case of tantrayana.

You can do whatever you want.  Just make sure that whatever you do, you give your whole life over in the effort.   One way destroys what is alive.  The other gives to life to a possibility that was dead.  i.e...

Case 5 Kyõgen's "Man up in a Tree"                   五　香嚴上樹
香嚴和尚云、如人上樹、口啣樹枝、手不攀枝、脚不踏樹。
Kyõgen Oshõ said, "It is like a man up in a tree hanging from a branch
  with his mouth; his hands grasp no bough, his feet rest on no limb.
樹下有人問西來意、不對即違他所問、若對又喪身失命。
Someone appears under the tree and asks him, 'What is the meaning of
  Bodhidharma's coming from the West?' If he does not answer, he fails
  to respond to the question. If he does answer, he will lose his life.
正恁麼時、作麼生對。
What would you do in such a situation?"

Mumon's Comment
無門曰、縱有懸河之辨、惣用不著。
Even if your eloquence flows like a river, it is of no avail.
説得一大藏教、亦用不著。
Though you can expound the whole of Buddhist literature, it is of no
  use.
若向者裏對得著、活却從前死路頭、死却從前活路頭。
If you solve this problem, you will give life to the way that has been
  dead until this moment and destroy the way that has been alive up to
  now.
其或未然、直待當來問彌勒。
Otherwise you must wait for Maitreya Buddha and ask him.

Mumon's Verse 頌曰
香嚴眞杜撰 Kyõgen is truly thoughtless;
惡毒無盡限 His vice and poison are endless.
唖却納僧口 He stops up the mouths of the monks,
通身迸鬼眼 And devil's eyes sprout from their bodies.

I like this answer. However, the Mumon's Verse appeared an incorrect translation of Chinese (if that's in Chiinese): 香嚴眞杜撰 Kyõgen is truly lying (杜撰 means writing a make-up story); 唖却納僧口 He shut up the mouth of mine the monk (納僧 is for a monk to call himself)

Huh.  I'll have to look a Sekida's translation and see what he wrote.  He's usually pretty good.  I just copied this from Sacred Texts because it was convenient.  "Lying" definitely makes more sense than "thoughtless"!

If you hear noises "hearing hearing hearing"   -- thinking it might be a bug crawling to the fire "worry worry worry"  or thinking*3
but if you see a bug crawling to the fire and know that its hapening for sure  - than practice karuṇā and metta and save him   -      stop the formal meditation mindfully  get up mindfully labeling all your actions and pick up the bug and put it far away - i wouldnt think it needs feeding but if you do than yes put him some water and food why not thats extra - no dont go to china  - you help him enough with common sense
than you get back to the formal practice  ....  but helping the bug is also part of the practice
and not helping the bug can come from aversion and greed and ignorance quite as easliy even if you are not aware of it

If Andrei is able to help the bug without kill countless by doing so, he might do it.
Better to do not light fire and lure being in wrong direction for ones indentification "I am a great helper" now not able to help himself get rid.
Maybe good to attend to a/the fire sermon.
One left house, in training or finished, working the best way for all being, has no duty to help.
But one should, now not left house, not directed to Nibbana, not keeping precepts and abstain from sensuality, not misuse ideas of anatta, anicca, sunnata to avoid the merits of giving if possible.
It's very common today that so called Dhamma practicing people neglect giving and duties (Sila) and use high Dhamma, yet not understoid as excuse. This is called kilesa mara. Some think "well that's his kamma" and yet forgetting the own kamma by wrong intention, words/no-words and deeds/no-deeds while acting based on greed/aversion/delusion with it.
If one has the possibility to help without harming at the same time others or him/herself or break basic precepts, there is seldom reason not to do.
For one doing such like most/many sample in the question, such is an ordinary fool, just counting how many he/she will harm, usually not able to walk two steps without crashing others and lighting fire all day long...
So first aways ones duties in a relation, precepts, being mindful and what is left to give, then give and let go.
Don't light fires of acquisitions, attracting food for your identification, a practice of fire worshipping, what esle is it good for then to nurish one ego, enlarging the fields of corpse.
And if actually really interested to understand where there is still doubt, on a heart to heart level, doors are always open.
That's the way precepts-gift then even with samadhi, with panna, are the greatest gifts, renouncing put into fires for the sake of becoming this or that. Such one is called to follow the wise, one on the eightfold path.
Why does one believe that the lightening of certain A-Dhamma and Mohayana attracts so many being? Nibbana? Or a huge fire assuming it for a refuge... now would a fire worshipper have enough fuel to continue if there are no bugs nurishing it?

The Blessed One, having known with his awareness the train of thought in the awarenesses of the 120,000 Magadhan householders and brahmans, addressed Uruvelakassapa in verse:
“Having seen what,
  while living at Uruvelā,
  has the teacher of ascetics,
  abandoned the fire?
I ask you about this matter, Kassapa:
  Why has your fire oblation been abandoned?”
[Uruvelakassapa:] “Forms, sounds, and flavors too,
  Sensuality and women — sacrifices promise these.
Having known of acquisitions: ‘This is stained,’
  I no longer delight in oblations or sacrifices.”[1]
(Mv.I.22.5) [The Buddha to Kassapa:]
  “Now your mind doesn’t delight,
  in forms, sounds, or flavors.
Then, in the world with its humans and devas,
  what is your mind’s delight? Explain it to me, Kassapa.”
[Uruvelakassapa:] “Having seen the state of peace,
  without acquisitions,
  having nothing,
  unattached in sensuality and becoming,
the state unchanging,
  leading to nothing else,
  I no longer delight in oblations or sacrifices.”

Now what's the questioners answer why not simply train Dana, Sila, Bhavana but busy in lightening fires and "safe" bugs?
It's good to increase samvega seeing on self as possible next bug and the misery of being bond to the sense and the world, then seeking for real light and put much effort into it.

Then, as the night was ending, the Blessed One, having consumed (the nāga’s) fire with (his own) fire — without damaging his outer skin, inner skin, flesh, tendons, bones, or bone marrow — put him in his bowl and showed him to Uruvelakassapa the coiled-hair ascetic, (saying,)
“Here, Kassapa, is your nāga. His fire was consumed by fire.”
The thought occurred to Uruvelakassapa, “He’s powerful, the great contemplative, and mighty, in that, with his own fire, he consumed the fire of the fierce nāga king — powerful, with poisonous fangs, terrifyingly poisonous! But still, he’s not an arahant like me.”

[Note: This is a gift of Dhamma, not meant for commercial purpose or other low wordly gains my means of trade and exchange]

Imagine you're at a resort hotel by the ocean for a week by yourself, looking out the windows thinking: coffee, coffee, when you decide to check in on the Buddhist site and notice Andrei's question crawling upwards in the stats...
I used to run a retreat center, and mice would get in and run around on the suspended ceiling above us while we meditated. This invariably happened most on the occasional evening when a guest or outside visitor was sitting with us. So embarrassing! We put live traps in the ceiling and caught the mice and drove them a ways off. Lots of effort and more came in. Sometimes a snake would be heard up in the ceiling, although guests did not know what that sound was. Eventually found the hole and plugged it.
I no longer run a retreat center. I do throw animals back in the sea when walking on the beach, or carry bugs outdoors if possible. But it is not a big dilemma. Every day when I take a shower, I must be killing multitudes of bacteria. That's life, just do what you can.

Was it really coffee, coffee, or beer, beer?

I do drink coffee every day, beer less often. Yesterday I came across another spiny urchin way up the beach, and another... Every 50 feet or so. I looked to see if they still lived then carried and threw in to the water again, wondering if they were  already too far gone, or if they were only on shore in the first place because they had been dying. Saw a man laying asleep, still unmoving hours later. Then later still, not there. Does the world need my meddling?


text:
What are the arguments behind the relatively late dating of Khuddaka Nikaya and Abhidhamma Pitaka?
It is generally told that the Khuddaka Nikaya is the latest among the five Nikayas of the Sutta Pitaka. Similary, the Abhidhamma Pitaka is also considered as the latest composition among the three Pitakas. It seems that these are universally accepted truths among the scholars of Buddhism. But what are the exact arguments behind these two assertions?

For the layer of pāli-canons timeframe, please see:
What are timeframe were pali canons, included commentaries, done, especially Mahavihara-Theravada?
The arguments began from misunderstanding of students/scholars in reading study system, especially from the western world, see  The Case of Dhammakaya (Thai: กรณีธรรมกาย) by P.A. Payutto.
Reading study system make students/scholars understand teaching discontinuous, incomplete, through the buddhist study course.
You can see through below cases that the arguments of buddhist hypothesis by the students/scholars in reading study system, began from misunderstanding.
So, there are many misunderstand appearing from the past and still going on now, below.
I have the evidences in pāli-canons for each below example, if someone request to me, I will add them to this answer as soon as I can.
for the example:
(a) The introduction of dhammasaṅgaṇī's commentary, by the tipitaka-memorizers, said:

sāriputta studied just the brief abhidhamma teaching from buddha. Then
sāriputta taught his advance literary abhidhamma to his large number
of  students.
(Sāriputta's student was included upāli because some paṭṭhāna-words appear in
Vinayapitaka Parivāra, and some abhidhammas' description appear
in vinaya, too. So, in gosiṅgasāla-sutta said many famous
bhikkhu go to listened sāriputta's teaching, and in A.N. Ekaka. buddha
announced sāripuuta is the best of teacher who can teach the listener
for enlightenment as alike as himself. But sāriputta's literary abhidhamma didn't appear directly in 4 first nikāya of suttanta because even though ānanda often went to listen sāriputta, but he was not sāriputta's close student. When the 1st saṅgāyanā began, the most of sāriputta's teaching, still kept by sāriputta's students, not by ānanda. So, the fact appeared in commentary which said that many canon in K.N. were taught by sāriputta. Another, K.N. and Abhidhamma are easier to memorize than suttanta, by technical, too. So, the very big amount of abhidhamma and K.N. in oral study sysytem are not an argument to said "abhidhamma began very late after buddha time".)

But the beginner students just read through commentary then misunderstood and distort it as "commentary said buddha taught abhidhamma".

(b) The introduction of kathāvatthu's commentary, by the tipitaka-memorizers, said:

The forth member, of sevent abhidhamma canons, were authored in 3rd saṅgāyanā.

But the beginner students just read through commentary then misunderstood and distort it as "abhidhamma authored in 3rd saṅgāyanā".

(c) In VN Pañcasatikakhandhaka, 1st saṅgāyanā saṅgha, the original commentary teachers, made the unanimous decision to keep, to modify not/to add not, all the buddha's speech rules in the Vinaya, even the lesser and the minor rules. If there are something to describe about vinaya, it must appear in the other's context, such as the upāli's sikkhāpadavibhaṅga/upāli's parivāra/commentary/etc., without any modify buddha's speech.
But the beginner students just read through some sutta, then misunderstood and distort it as "there were just 150 vinaya rules in vinaya pitaka".

(d) Commentary said in introduction of D.N.'s  commentary:

Ānanda showed to kassapa, at 1st saṅgāyanā, that he did not modify anything of every sutta which he was presenting  to 1st saṅgāyanā saṅgha.

But the beginner students just read through the english translation version of 4 nikāya, which translated only some part, then misunderstood and distort it as "some sutta in 4 nikāya maybe authored after 1st saṅgāyanā".

(e) Vinaya pitaka and DN's commentary, the tipitaka-memorizers, said:

1st saṅgāyanā saṅgha gave each nikāya and commentary to 5
arahanta-groups at 1st saṅgāyanā meeting cave, upāli school got
vinaya-pitaka, ānanda school got dīghanikāya, etc, to recite for
the received nikāya, and there were somebodies in each school memorized more than 1 nikāya, too. Then about each 100 years later their relayed
students met each other school members again to recite them together,
2nd and 3rd saṅgāyanā, again. Each saṅgāyanā, they did it on the same
rule in (c) and (d).

But the beginner students just read through the western scholars' thesis, who never recite and memorize tipitaka, then misunderstood and distort it as "saṅgāyanā was the meeting to edit tipitaka." And "tipitaka become blurred through the time, because of oral study system".

You can see through above cases that the arguments of buddhist hypothesis by the students/scholars in reading study system, began from misunderstanding.


text:
Understanding beginningless
I often see the word beginning-less in Buddhist readings and on this site but how do I try to understand this concept being the ignorant human being I am?

Is it just a metaphorical way to describe a very long time?
Is it like the saying which came first: the egg or the chicken in which the answer ‘doesn’t matter’ since they’re both here in the now?
Or is it what we experience is an illusion created from our ignorance therefore there is no real beginning.

Scientists say our universe is roughly about 13.8 billion years old so there is probably a beginning? I am not accepting they are correct but not denying the fact either.
I feel like when people use the word beginning-less, they are using it as an excuse to explain something that is “unexplainable” because how can something be beginning-less?Is it futile to try to grasp this concept? Or if this concept is understandable what can I do to see this?

I have not read the term "beginningless" in the Pali suttas, which refers to a "beginningless beginning", similar to chicken vs egg.
The Pali suttas use the phrase: "without discoverable beginning", which means a first occasion cannot be discerned.

Bhikkhus, this is said: ‘A first point of ignorance, bhikkhus, is not seen such that before this there was no ignorance and afterward it
  came into being.’ AN 10.61

Bhikkhus, this saṃsara is without discoverable beginning. A first point is not discerned of beings roaming and wandering on hindered by
  ignorance and fettered by craving. SN 22.99

In other words, "ignorance", for example, is the present 1st cause for the manifestation of suffering. Here, Buddhism does not attempt to answer the question: "What came before or what causes ignorance?". This is why the term: "without knowable beginning" is not analogous to the chicken vs egg scenario. The Pali suttas are saying: "It is not knowable when ignorance 1st began or what caused it however ignorance exists in the present moment that causes suffering".
Therefore, Buddhism does not affirm or deny the 'physical universe' (which is not the meaning of 'samsara') may have had a beginning, such as the Big Bang (despite the illogicalness of the Big Bang theory).

Anamataggoyaṃ bhikkhave saṃsāro. http://dsalsrv02.uchicago.edu/cgi-bin/philologic/getobject.pl?c.0:1:715.pali

I take it that's a reference to (what is translated as) this phrase, which appears in several suttas including for example the "Assu Sutta: Tears (SN 15.3)":

From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries — enough to become disenchanted with all fabricated things, enough to become dispassionate, enough to be released.

I won't answer your literal questions but here are a few comments.

Buddhism teaches that conditioned things are impermanent ... that anything which begins because of some cause (i.e. because the conditions for its existing have come together) will have an end when those conditions no longer apply.
So, it's interesting to know the cause (or beginning) of suffering: because knowing how or when it begins is a hint as to when or how it end (for example if a fire starts when there is heat and fuel, it ends when there's no heat or no fuel, or when heat is detached from fuel).
But samsara doesn't seem to have a beginning, doesn't have a "construable" beginning (and may continue endlessly). Even so it may be possible to escape it, to find release: by becoming dispassionate and disenchanted with fabricated things (also known as "conditioned things").

The Buddha could see his (and other people's) past existences, so the question ("how did it all begin?") was likely to arise (and people, maybe your physicists for example, still ask themselves that to this day).
But this ("How did the world begin? Did the world begin?") belongs to the category of unanswered questions.
When I was young I used to fight with my brother, and when my mum would come then we'd say, "He started it!" -- "No, he started it!", and she'd tell us, "It doesn't matter who started it, you both have to stop."
See also "a thicket of views" on this page which helps to explain why unanswered questions are unanswered.
See also for example the first few lines of the Dhammapada (including this verse), which suggest it doesn't matter whether you have a reason for fighting, what matters is whether you hold (attach to) that view.
Anyway, saying that the beginning is "inconstruable" is a way of answering (or not answering) the question, of closing that line of investigation.
The decision of what to investigate, of what to teach as dhamma, is a question of soteriology (see also "Simsapa Sutta: The Simsapa Leaves (SN 56.31)").

Finally, you say, "our universe is roughly about 13.8 billion years old".
I think that the antique cosmology assumed that the "world" is cyclic, subject to expansion and contraction. Perhaps there was another universe before this one, and another one after? It's inconstruable...
I want to say though that I don't think that Buddhism and Physics (including both astrophysics and quantum physics) are describing the same phenomena. I think that Buddhism is primarily a description, not of "the world" but of our perception of the world, of (our) consciousness, of man's relating to the world (including ethics and wisdom, etc.).
Anyway I think this description (i.e. that its beginning is inconstruable) isn't exactly being applied to "our universe": in the original context it's a description of "transmigration" i.e. of samsara.

In a comment, Samana Johann pointed out that the Pali phrase is:

Anamataggoyaṃ bhikkhave saṃsāro.

Here are dictionary definitions:

Definitions for anamatagga
New Concise Pali English Dictionary
  anamatagga
  mfn.
  without beginning (or end, generally of saṃsāra).
Concise Pali English Dictionary
  anamatagga
  adjective
  one whose beginning is unknown.
PTS Pali English Dictionary
  anamatagga
  adjective
  epithet of Saṃsāra “whose beginning and end are alike unthinkable”, i.e., without beginning or end. Found in two passages of the Canon SN.ii.178, SN.ii.187 sq. = SN.iii.149, SN.iii.151 = SN.v.226, SN.v.441 (quoted Kv.29, called Anamatagga-pariyāya at Dhp-a.ii.268) and Thig.495, Thig.6. Later references are Cnd.664; Pv-a.166; Dhp-a.i.11; Dhp-a.ii.13, Dhp-a.ii.32; Sdhp.505. [Cp. anāmata and amatagga and cp. the English idiom “world without end” The meaning can best be seen, not from the derivation (which is uncertain), but from the examples quoted above from the Saṃyutta. According to the Yoga, on the contrary (see e.g. , Woods, Yoga-system of Patañjali, 119) it is a possible, and indeed a necessary quality of the Yogī, to understand the beginning and end of Saṃsāra].
ana (= a neg.) + mata (fr. man) + aggā (pl.). So Dhammapāla (avidit-agga Thag-a.289); Nāṇakitti in Ṭīkā on Dhs-a.11; Trenckner, Notes 64; Oldenberg Vin. Texts ii.114. Childers takes it as an + amata agga, and Jacobi (Erzähl. 33 and 89) and Pischel (Gram. § 251) as a + namat (fr. nam) + agga. It is Sanskritized at Divy.197 by anavarāgra, doubtless by some mistake Weber, Ind. Str. iii.150 suggests an + āmrta, which does not suit the context at all

I infer from the PTS definition, that:

The derivation/etymology of the word is uncertain, people understand it from the examples (context) in which it is used.
It can be contrasted with the Yoga Sutras of Patanjali, which (according to the PTS) say that it's possible and necessary "to understand the beginning and end of Saṃsāra", and which (according to Wikipedia) is about the same time as the Buddha (400 BC).
I think that scholars find that there are various little bits of Dhamma which contrast other Dhammas (e.g. Brahminism, Jainism), as if the clarify sometimes ways in which Buddhist Dhamma differs from other dhammas.

There seems to be a contradiction, where it was said: "The Buddha could see his (and other people's) past existences...". If Buddha could see past existences, he could see the very 1st. Also, there is no evidence for this idea, it is not something that falls within the definition of "Dhamma" (namely, visible here & now; verified by the wise).

I had to score this post down because it provides no quotes from the suttas that substantiate the idea that: "Saṃsāra “whose beginning and end are alike unthinkable”, i.e., without beginning or end. ". The suttas obviously teach the end of samsara.

Sure. But I think you need to substantiate the views of the Pali dictionary complied by British scholars, which you seem to have given the impression is the view of the Buddha. Is the view of the dictionary that of the Buddha or that of Buddhaghosa found in the Visuddhimagga?

I don't know, only that it's the view of the dictionary. Every translator seems to translate it similarly (including the version you quoted: "without discoverable beginning"), so I have no reason to doubt them/everyone. The dictionary says that the derivation (etymology) is unclear, so I can't hope to understand the word from its etymology, and that people understand it from the examples (context) of its use.

I am not disagreeing with "without discoverable beginning". I am disagreeing with the dictionary idea of "without end", which I have never read, apart from in the Visuddhimagga.

cp. the English idiom “world without end” is part of the quoted dictionary definition and is otherwise not relevant to this answer nor the OP's question. The earlier paragraph, which started But samsara doesn't seem to have a beginning and includes the word endlessly, was mine (not the dictionary's nor Buddhaghosa's): trying to explain why a beginning, a condition, a cause, might be interesting/relevant.


text:
What are the different Buddhist views on marriage?
I know that marriage is a secular event in Buddhism, but what are the different attitudes are there for or against marriage? And what type of Buddhists(Theravada, Mahayana, Sangha, Lay etc)  claim these views?

The Pali scriptures say:

Parents have a duty to arrange or find a suitable marriage partner for their children (DN 31); therefore marriage appears to be viewed favorably (for non-monks) in the Pali scriptures.
A suitable marriage partner in one that shares four qualities (AN 4.55).
In marriage, a husband serves his wife & gives the wife authority in the home. (DN 31)
There are seven kinds of wives (AN 7.6).
Marriages where one or both partners do not follow the five precepts & do not practice unselfishness are doomed for problems &/or failure (AN 4.53).
Difficult is life as a monk; difficult is it to delight therein. Also difficult and sorrowful is the household life. (Dhp 302)

It is the effect of ones past kamma is one of the determinant factors that influences the nature of ones present situation in life. For instance for somebody, only when s/he gets married that for him/her all hell would break loose and the marriage end in divorce. That person can never find contentment in marriage even in subsequent marriages to others. Then there are those who can never find success as a recluse/bhikku. That is their Kamma. Thus from a Buddhist standpoint, our present mental, intellectual, moral and temperamental differences are mainly due to our own actions and tendencies, both past the present.


text:
Whether knower disappears automatically after doer disappeared?
Did   meditation; when concentration  on the  breath at the tip of the  nose  suddenly  controller has disappeared and cittarupa came without  control.Is it a stage  that knower  and doer disappeared?after the experience  feel like no self at that time.

Did meditation; when concentration on the breath at the tip of the nose suddenly controller has disappeared and cittarupa came without
  control.

Cittarupa always functions by itself. The idea of a "controller" is an illusion created by delusion, ignorance, clinging & craving.

Is it a stage that knower and doer disappeared? after the experience feel like no self at that time.

Yes. When the sense of knower & doer disappear, this is insight into anatta (not-self) of the five aggregates. The five aggregates operate on their own, without a self controlling them.

Is this the place where called it as non occurrence?

Strictly speaking, awareness of the knower and doer disappear only during the meditative state of samadhi, including the experience of sunyata in samadhi. But there are many states of samadhi. They disappear together in any case. In the Theravadin tradition the experience of the knower remains present during vipassana or insight meditation and also during Nibbana. In Theravadin Buddhism, insight into no-self is a relative truth and not an experience of samadhi. In Mahayana Buddhism, the experience of no-self occurs only during the experience of sunyata, making no-self an absolute truth. Nibbana and sunyata are not the same thing.
Ordinarily, “concentration on the breath at the tip of the nose” is a part of vipassana practice. However, depending upon one’s karma, a person can easily slip into a state of full samadhi.
You seem to be mixing the Theravadin and Mahayana teachings, which can be confusing.

The Buddha tried to show us the inherent unsatisfactoriness of all that constitutes a human being, so that we make real effort to get out of the wheel of birth and death. We have to understand that there is no individual who owns body, feeling, perception, thought and consciousness. That is the most difficult aspect of the Buddha’s teaching. Difficult to conceptualize and even more difficult to experience. Without meditation, it will remain an intellectual exercise. Even in meditation only if you are a’Sotapanna’ / Stream Entrant, will you l get to understand that there is the deed, but no doer.


text:
Why don't monks get married?
If there are no restrictions in Buddhism then why do they not want to get married?

Of course there are restrictions!

Abrahmacariya veramani sikkhapadam samadiyami (I will refrain from sexual activity)

If you can't have sex, your spouse probably won't be too pleased.  Having a family of your own will also prove slightly more difficult.  Besides, the whole point of forgoing the householder life for homelessness is to pursue enlightenment with the minimal amount of obstacles possible.  Supporting a family is quite a large responsibility to undertake!
(Note: this does not apply to all Buddhist schools.  Zen monks often marry.  But if you are looking for the strict, scholastic answer, see above.)

Then does it make enlightenment harder to achieve for the Buddhists who are married? Isn't enlightenment their goal aswell?

It may not make it harder, but it definitely doesn't make it easier.  It's like working two full time jobs. It's possible, but it's not going to be fun; you also just wouldn't have the time necessary to truly succeed at both. And not all Buddhist have enlightenment as their goal. In fact, at the time of the Buddha, only monks meditated! Householders were more often concerned with generating merit and a better rebirth. Having lay people take a run at enlightenment is a very recent development (the Vimalakirti Nirdesa Sutra aside- and you can't tell me that his looks like a modern lay practice!)

"Zen monks often marry." should be only Japanese monastery life by/after Meiji Modernization, when Western ideologies introduced after the defeat of East in war. Should refer to history. Monk = Bhiksu/Bhikkhu means celibacy, renunciated from household life incl. marriage

See also What's the difference between monks and priests? (for further info about monastics in Japan).

My own Obaku lineage technically comes from China.  Some of our Chinese monks are married, but then again, there is a huge Japanese influence in our school.  Believe it or not, there are some examples of married monks prior to the Meiji.  There is some evidence of married monks going back to the Kamakura (~1100-1300)!  And IDK.  What one tradition calls a monk is really up to that tradition; no sense in arguing the point as they are the ones writing the definition.

Some do get married! It just depends on the tradition.
In the 2005 article "I married a monk" the excerpt below speaks of some notable examples

Finally, the master spoke in a sermon-like tone, looking off into the distance. “There are precedents and justifications for marriage in Buddhism,” he said. “A famous monk, Manhae, was known for his love poems, which many say could not have been written had he not loved a woman deeply. Then there is the seventh-century monk Wonhyo, the most famous monk in Korean Buddhism. It’s said that the king asked him to sleep with his daughter, the princess, to console her. Wonhyo saw this as skillful means. In the Tripitaka, there are examples of the Buddha in dialogue with householders. He teaches how householders can live a pious life.”

If you read the entire article you will find the master struggled to come to this view, and at first was opposed to the marriage. A typical battle of tradition vs modern life.
This case was a Korean Zen monk but other traditions have a place for marriage for those that want it.
In Tibetian Buddhism Monks and lamas don't necessarily have to be celibate, and sometimes get married.
In Japan monks and nuns can marry as well.
Different Traditions and vow sets have different rules.
I believe that the other traditions all have a vow of celibacy, but please correct me if I am wrong.
One interesting thing to note, for those who do take the vows, is that sexual misconduct for monks and nuns holding the vows includes masturbation.


text:
Is samsara without end?
I read the following in the PTS Pali dictionary:

Saṃsāra "whose beginning and end are alike unthinkable", i. e., without beginning or end.

Are there any Pali suttas that support this view of endless samsara without an end?

What do you mean by end of Samsara? Do you mean to say that Samsara ends if it becomes uninhabitable ? Or do you mean to say that Samsara ends if it vanishes into space?

If something is unthinkable, why try to think about it?

Well, from Mahayana perspective it's both. Samsara is endless, just like Dukkha is an invariant principle of sentient existence. Accepting Dukkha (here, inherent unreliability) of phenomena makes it Tathata, suchness. Accepting Samsara makes it Nirvana. Does not mean Samsara has ended or Dukkha ended - not at all. We just make an end to it (nirodha, 3rd N.T.). Endlessness of Samsara is one thing you can truly rely on, which makes it unconditional Nirvana.
Now, if I forget all that and just reason from the original sources, here is what I get:
Looking at your PTS dictionary quote, they are talking about Anamatagga (without beginning / without end) being an epithet of Samsara. When I search Sutta Central for "anamatagga" I find for example this verse from Therigatha:

"...Long are the foolish in Samsara,
  again and again cry
without beginning, without end, over the father's death,
  the slaughter of the brother and the murder of the self.
Oh tears, breast milk and blood:
without beginning, without end you run in Samsara!
  Remember the wanderings of the creatures
  and the way the bones pile up!
Remember the four oceans,
  filled with tears, mother's milk and blood!
  Remember in one epoch
  bones heap up like mount Vepulla!
Without beginning, without end have you flowed (lit. samsara’ed),
  endless like the seeds of jujube fruit. ..."

This, combined with the literal meaning of the word "samsara" - "running by itself", "drifting" can point us in the right direction. Samsara is endless unless we put an end to it (nirodha). And how do we put an end to it? By applying the principle of this/that-conditionality and undoing the 2nd noble truth, i.e. by accepting what is and arriving at tathata. Now technically, what we accept is not really Samsara as it is, that would be surrendering. Instead, we learn to see Shunyata and that's what we accept, Samsara-as-Shunyata. Does not mean that Samsara has gone anywhere though, it is still endless as it always were. In fact, if we want to help other sentiment beings, we have to deal with Samsara every day.

A sutta like this ("the skeletons of a single person, running on and wandering in samsara for an aeon, would make a heap of bones, a quantity of bones as large as this Mount Vepulla") or this ("would that blind sea-turtle, coming to the surface once every one hundred years, stick his neck into the yoke with a single hole") implies that it may be (or may have been) a very long time indeed.
It's not clear whether that long time is past, future, or present.
IMO the implication is that it has been a very long time in the past, and that unless you start the follow the Buddha's way (for liberation) it will continue indefinitely (until you do).
The question of whether it's literally endless may be another of the unanswered questions ("Is the cosmos eternal?").

The sutta states But when one sees with perfect wisdom
The four noble truths as they are —
Suffering, the origin of suffering,
The overcoming of suffering,
And the noble eightfold path
Leading to relief from suffering —
Having merely run on
Seven times at the most,
By destroying all fetters
One makes an end of suffering.

The answer
"Anamataggo" word is in S.N. Nidanavagga = cause = paṭiccasamuppāda = cycle loop of causes and effects.
You must recite and memorize it's pāli, before you ask something about pāli. The answer already appear in sutta sequence, but you overlook it because you never recite and memorize it's original pāli.
The analysis of anamatagga word
Why the translators try to translate like that?
Because of pāli context of this sutta forcing them to do like that.
Pāli's sutta:

"Anamataggoyaṃ, bhikkhave, saṃsāro. Pubbā koṭi na paññāyati avijjānīvaraṇānaṃ sattānaṃ taṇhāsaṃyojanānaṃ sandhāvataṃ saṃsarataṃ."

The translators must describe "Anamataggo" like:

"Anamataggoyaṃ bhikkhave, saṃsāro == Pubbā koṭi na paññāyati avijjānīvaraṇānaṃ sattānaṃ taṇhāsaṃyojanānaṃ sandhāvataṃ saṃsarataṃ."

So, in commentary:

anamataggasaṃyuttassa paṭhame anamataggoti anu amataggo, vassasataṃ vassasahassaṃ ñāṇena anugantvāpi amataggo aviditaggo, nāssa sakkā ito vā etto vā aggaṃ jānituṃ, aparicchinnapubbāparakoṭikoti atthoฯ saṃsāroti khandhādīnaṃ avicchinnappavattā paṭipāṭiฯ pubbā koṭi na paññāyatīti purimamariyādā na dissatiฯ yadaggena cassa purimā koṭi na paññāyati, pacchimāpi tadaggeneva na paññāyati, vemajjheyeva pana sattā saṃsarantiฯ

However, some pāli students maybe over worry about "how to make 'anamatagga' by kaccāyanasutta (ancient pāli grammar cannon)", then they will be stuck their  thinking with anamatagga's ingredients. This is just the first rule of vicayahāra in netti-pakaraṇa cannon, pada-vicaya. But commentary can going on by next rule of vicayahāra in netti-pakaraṇa cannon, pubbāpara-vicaya, then use "54, 60 jinavacanayuttaṃ hi" and "404, 370. tesu vuddhilopāgamavikāraviparītādesā ca" of kaccayanasutta to translate 'anamatagga'.
So, if you recited and memorized pāli, first, you will know this process and leave out of being stuck in pāli's ingredient.


text:
Can a one-pointed mind and a unified mind alternate?
During meditation i notice that the mind tends to alternate between one-pointedness (breath touching the tip of the nose while breaking off any upcoming thought) and classifying upcoming thoughts into thoughts about the past, future and related to ego, before breaking off the thought, or observing the upcoming and cessation of all sensations in the realm of body and mind while always keeping adhithanna in posture. Is this inconsistent or can a unified and one-pointed mind exist alternately or even simultaneously?

It's either one or the other.  One-pointedness means exactly that - the mind is fixed in one place.  Anything apart from that single point detracts from concentration.  What can happen is that as you develop one-pointedness, your attention can get somewhat "smeared".  You'll still have some hold of the single point, but your attention isn't fully fixed on it.  In this case, your vitakka or applied thought is [mostly] there, but your vicara (e.g. sustaining thought) is either slipping around or is intermittent.
If you find yourself moving away from single-pointedness on a fixed object, my best advice is to switch to something a little less subtle like the full inhalation and exhalation as it travels through your body.  It is much easier to maintain sustained attention on something that is moving.  In a sense, the motion keeps your interest more than would a single point.  As your concentration deepens, you can begin watching the where the breath makes contact again.
Bonus point - don't watch the breath, wait for the breath.  What I mean by that is that your attention should be passive as if you were waiting for a train to arrive, a gaggle of geese to cross the road, or your Hot Pocket to cook in the microwave.  Westerners especially can be overly aggressive when they actively try to watch the breath.  The pin the poor thing down with their efforts and don't give it any room to...well...breath.  As the Hsin Hsin Ming puts it, "when you try to achieve passivity, your very effort fills you with activity".  Strong arming your attention like that arouses needless agitation.  If you take a more patient approach, your concentration will be correspondingly deeper.


text:
Concept of Vedana as expounded in Theravada Buddhism
Throughout canonical discourses (Sutta Pitaka) the Buddha teaches that there are 3 modes of Vedana.
Where in Pali canon do we find 6 classes of Vedana?
How is Vedana related to Nibbana?

Vēdanā is conventionally translated as “feelings”, but it is much more than just feelings. The Buddha said that vēdanā can be analyzed in many ways, with simple or deeper meanings. Though you have been told that there are six types of Vēdanā  there are actually 9 types of vēdanā.
A vēdanā can be a dukha vēdanā (due to a past bad kamma), a sukha vēdanā (due to a past good kamma), or a neutral sensation — like feeling the wind on the body — called an upekkha vēdanā. However, normal humans go far beyond that and generate three additional types of their own mind-made “samphassa ja vēdanā”.
A normal human being will mentally generate three more type of vēdanā due to those sukha, dukha, and neutral vēdanā that initially arise due to kamma vipāka via all five physical senses. If it is dukha vēdanā (due to a headache, getting injured, etc. ), one is likely to start worrying about it and add more suffering. Those are dōmanassa vēdanā or āmisa dukha vēdanā.
If it is sukha vēdanā (getting a massage, lying in a luxurious bed, etc. ), one is likely to start generating thoughts about how good it is and how one can enjoy similar sukha vēdanā in the future. Those are sōmanassa vēdanā or āmisa sukha vēdanā ; one could also be generating them by remembering past such sukha vēdanā. These are also added in by the mind. Sōmanassa means “mind-made joyful”. Dōmanassa means “mind-made misery”, which is basically a depressed mindset.
When one stays away from generating too many “samphassa jā vēdanā” of both kinds, one will start feeling three more types of vēdanā. These are called nirāmisa vēdanā, because they arise due to staying away from cravings (and repulsion) to worldly objects. When one prevents the mind from heating up by comprehending the adverse effects of “san” and staying away from them, one’s mind starts “cooling down”. This is the nirāmisa sukha vēdanā. This is what is emphasized by “ätäpi sampajäno” in the Mahā Satipatthāna Sutta; it means “remove the fire or heat from one’s mind by being aware of the ‘san‘ or “immoral tendencies”.
Then there are vēdanā that one experiences when proceeding on the Noble Eightfold Path. Sometimes, one gets a bit discouraged by not advancing “fast enough” on the Path.  Those are not dōmanassa vēdanā (because they are devoid of patigha anusaya); they are nirāmisa dukha vēdanā.
The Sutta references are many, and I will refer you to one – the Ananda Sutta: Leading to Awakening (SAMYUTTA NIKAYA 12:10).
How vēdanā is related to Nibbana will call for a lengthy explanation, and you will not understand it if explained it in a paragraph or two. One day you will get to understand it proper, if you try to make sense of the following:
“Sukha and dukha vedana arise due to kamma vipaka. Somanassa and domanassa vedana arise due to sankhara, which in turn arise due to our gathi and asavas. The more sankhara we do, the stronger a given gathi (habit) becomes, which in turn become asavas (cravings) and fuel the sansaric journey (rebirth process). This vicious cycle can be broken only through comprehending the anicca nature of this world.”

Comments are not for extended discussion; this conversation has been moved to chat.

There are three basic vedana (feelings), namely:
(i) pleasant;
(ii) unpleasant; &
(iii) neither-pleasant-nor-unpleasant;
as follows:

And why, bhikkhus, do you call it feeling? ‘It feels,’ bhikkhus, therefore it is called feeling. And what does it feel? It feels
  pleasure, it feels pain, it feels neither-pain-nor-pleasure. ‘It
  feels,’ bhikkhus, therefore it is called feeling. SN 22.79

However, often these three feelings are discussed in different ways, such as:

And what, bhikkhus, is feeling? There are these six classes of feeling: feeling born of eye-contact, feeling born of ear-contact,
  feeling born of nose-contact, feeling born of tongue-contact, feeling
  born of body-contact, feeling born of mind-contact. This is called
  feeling. SN 12.2

I have spoken of two kinds of feelings by one method of exposition; I have spoken of three kinds of feelings by another method of exposition; I have spoken of five kinds of feelings … six kinds of feelings … eighteen kinds of feelings … thirty-six kinds of feelings by another method of exposition; and I have spoken of one hundred and eight kinds of feelings by still another method of exposition. AN 36.22

Vedana is not related to Nibbana because Nibbana (the unconditioned element) is not a feeling (a conditioned element). Nibbana is non-attachment towards feelings (MN 37).

Here a bhikkhu is an arahant, one whose taints are destroyed, the holy life fulfilled, who has done what had to be done, laid down the
  burden, attained the goal, destroyed the fetters of being, completely
  released through final knowledge. However, his five sense faculties
  remain unimpaired, by which he still experiences what is agreeable and
  disagreeable and feels pleasure and pain. It is the extinction of
  attachment, hate, and delusion in him that is called the
  Nibbāna-element. Iti 44

Here, ruler of gods, a bhikkhu has heard that nothing is worth adhering to. When a bhikkhu has heard that nothing is worth adhering to, he directly knows everything; having directly known everything, he fully understands everything; having directly known everything, he fully understood everything, whatever feeling he feels, whether pleasant or painful or neither pleasant or painful, he abides contemplating (observing) impermanence in those feelings, contemplating (observing) fading away, contemplating (observing) cessation, contemplating (observing) relinquishment (letting go). Contemplating (observing) thus, he does not cling to anything in the world. When he does not cling, he is not agitated, he personally attains Nibbana. He understands: ‘Birth is destroyed, the holy life has been lived, there is no more coming to any state of being.’ Briefly, it is in this way, ruler of gods, that a bhikkhu is liberated in the destruction of craving, one who has reached the ultimate end, the ultimate security from bondage, the ultimate holy life, the ultimate goal, one who is foremost among gods and humans. MN 37

The Wisdom Library has provided an excellent reply to your first question. See https://www.wisdomlib.org/definition/vedana. For a definition of Nibbana, see https://www.wisdomlib.org/definition/nibbana.
When I visited Rumtek Monastery in Sikkim, India, to see the late 16th Karmapa some 30 years ago, a Tibetan friend told me that, according to Tibetan Buddhism, infants (including his own, who had just been born) are born Enlightened. This observation is neither affirmed nor denied in the Theravadin teachings. The feelings of a newborn infant are truly extraordinary, in my experience.

Paticca-samuppada-vibhanga Sutta:

Dwelling at Savatthi... "Monks, I will describe & analyze dependent
  co-arising for you.
"And what is dependent co-arising? From ignorance as a requisite
  condition come fabrications. From fabrications as a requisite
  condition comes consciousness. From consciousness as a requisite
  condition comes name-&-form. From name-&-form as a requisite condition
  come the six sense media. From the six sense media as a requisite
  condition comes contact. From contact as a requisite condition comes
  feeling. From feeling as a requisite condition comes craving. From
  craving as a requisite condition comes clinging/sustenance. From
  clinging/sustenance as a requisite condition comes becoming. From
  becoming as a requisite condition comes birth. From birth as a
  requisite condition, then aging & death, sorrow, lamentation, pain,
  distress, & despair come into play. Such is the origination of this
  entire mass of stress & suffering.
"Now what is aging and death? Whatever aging, decrepitude, brokenness,
  graying, wrinkling, decline of life-force, weakening of the faculties
  of the various beings in this or that group of beings, that is called
  aging. Whatever deceasing, passing away, breaking up, disappearance,
  dying, death, completion of time, break up of the aggregates, casting
  off of the body, interruption in the life faculty of the various
  beings in this or that group of beings, that is called death.
"And what is birth? Whatever birth, taking birth, descent,
  coming-to-be, coming-forth, appearance of aggregates, & acquisition of
  [sense] media of the various beings in this or that group of beings,
  that is called birth.
"And what is becoming? These three are becomings: sensual becoming [5 aggregates],
  form becoming [5 aggregates], & formless becoming [4 aggregates]. This is called becoming.
"And what is clinging/sustenance? These four are clingings: sensuality
  clinging, view clinging, precept & practice clinging, and doctrine of
  self clinging. This is called clinging.
"And what is craving? These six are classes of craving: craving for
  forms, craving for sounds, craving for smells, craving for tastes,
  craving for tactile sensations, craving for ideas. This is called
  craving. [see samudayasacca and nirodhasacca in saccapabba of mahāsatipaṭṭhānasutta]
"And what is feeling? These six are classes of feeling: feeling born
  from eye-contact, feeling born from ear-contact, feeling born from
  nose-contact, feeling born from tongue-contact, feeling born from
  body-contact, feeling born from intellect-contact. This is called
  feeling.
"And what is contact? These six are classes of contact: eye-contact,
  ear-contact, nose-contact, tongue-contact, body-contact,
  intellect-contact. This is called contact.
"And what are the six sense media? These six are sense media: the
  eye-medium, the ear-medium, the nose-medium, the tongue-medium, the
  body-medium, the intellect-medium. These are called the six sense
  media.
"And what is name-&-form? Feeling, perception, intention, contact, &
  attention: This is called name. The four great elements, and the form
  dependent on the four great elements: This is called form. This name &
  this form are called name-&-form.
"And what is consciousness? These six are classes of consciousness:
  eye-consciousness, ear-consciousness, nose-consciousness,
  tongue-consciousness, body-consciousness, intellect-consciousness.
  This is called consciousness.
"And what are fabrications? These three are fabrications: bodily
  fabrications, verbal fabrications, mental fabrications. These are
  called fabrications.
"And what is ignorance? Not knowing stress, not knowing the
  origination of stress, not knowing the cessation of stress, not
  knowing the way of practice leading to the cessation of stress: This
  is called ignorance.
"Now from the remainderless fading & cessation of that very ignorance
  comes the cessation of fabrications. From the cessation of
  fabrications comes the cessation of consciousness. From the cessation
  of consciousness comes the cessation of name-&-form. From the
  cessation of name-&-form comes the cessation of the six sense media.
  From the cessation of the six sense media comes the cessation of
  contact. From the cessation of contact comes the cessation of feeling.
  From the cessation of feeling comes the cessation of craving [saupādisesa-nibbāna]. From the
  cessation of craving comes the cessation of clinging/sustenance. From
  the cessation of clinging/sustenance comes the cessation of becoming [anupādisesa-nibbāna=no clinging aggregates anymore].
  From the cessation of becoming comes the cessation of birth. From the
  cessation of birth, then aging & death, sorrow, lamentation, pain,
  distress, & despair all cease. Such is the cessation of this entire
  mass of stress & suffering."