Is 爱 limited to people? What&#39;s the meaning of the first part of: 他爱怎么想就怎么想，我才不在乎呢

and 

Is &quot;我爱辣&quot; (Wǒ &#224;i l&#224;) a correct/understandable/idiomatic way of saying I like my food spicy?

suggest that 爱 can be used for things and abstractions, but that it may not be idiomatic.

Would it be common, sometimes, or never for pets?  Other animals?  Hobbies?  etc.
this is my first answer on this website.

他爱怎么想就怎么想,我才不在乎呢  = whatever he thinks/would like to think, I don't care.
In this sentence, 爱 is generally can be understanded as "would like". 
I prefer to say 我爱吃辣(I love eating spicy food) insted of 我爱辣
If you just only say 我爱辣, people may get confused when they hear this.

爱 can be used for things/hobbies etc, but a verb often followed by 爱。Examples: I love sports = 我爱运动。 I love playing basketball =我爱打篮球。 I love playing games = 我爱玩游戏。

Sometimes, you can use 爱 for pets and animals. However, I prefer to say 喜欢. Examples: 我喜欢动物。我喜欢小狗。 我喜欢小猫。