Character layout in calligraphy e.g. with respect to a quotation from Confucius I recently attended a brief introductory workshop about calligraphy at a Confucius Institute. The instructor, who also teaches at the local university and is both a calligrapher and painter from China, pointed out the calming, almost meditative effect of exercising the art form.

From the perspective of my own very limited experience I do agree. I liked both the Tang poetry that served as templates and the visual aesthetics of the resulting calligraphy (esp. the teacher's work). One thing that appeared to be typical was an approx. 5  x 5 matrix arrangements (one matrix, or two next to each other) of the Chinese characters in the poems.

Here's my question: if I tried some more calligraphy of my own (and I might, because of the enjoyable experience and because it would help this beginning student of Chinese to internalize the written characters) I would chose Confuicius' "At fifteen my heart was set on learning .." (吾十有五而志於學，三十而立，四十而不惑，五十而知天命，六十而耳順，七十而从心所欲，不逾矩。)

It's apparently not 5 x 5, but rather 8 + 4 + 5 + ..., it's not from a poem, and it's considerably older than Tang poetry, but is there still also a traditionally right way to present it on a single sheet of paper (e.g. in the context of calligraphy)? How would that appear?
It looks there are quite a bit of concepts in your question.


Tang poetry. Typical Tang poetry style is 5x4 or 7x4, with a bit more variations.
Layout of Chinese calligraphy. It's not necessarily 5x5. Don't be limited to that. Any size is okay. The typical layout is top to down, and right to left. For the layout of your mentioned Confucius, just write it as this layout with same characters in each column, without punctuations.
Best script for starter. The "calm" effect comes mostly from "Regular scripts", which is recommended for beginner, even for experienced ones.
Recommended process. I suggest you to copy 颜体（颜真卿）from the beginning, instead of writing your own. This is the most famous and respected Regular scripts. But I'm not a calligrapher. The teacher may has better and more specific recommendations.