Your first example is typical informal spoken English. Though it is colloquial, I should hesitate to use it in a written or formal context; others might disagree.
As you surmise, the second example means exactly the same thing - that he acts in a manner indicating that.... - but is more formally stated. An alternative to He acts as if... is He acts as ...
There is not much difference. When discussing two alternative possibilities or outcomes, one of which must occur, 'either' can be omitted. If it is included, it adds emphasis.
We can use either...or to emphasise a choice. (Either…or is used to
refer to two things or people.) In most cases 'either' can be omitted.
The idea [that war is obsolescent] may seem preposterously utopian.
That war is obsolescent is a declarative content clause. It says what the contents of that idea are, as it were. Content clauses are also called noun clauses.
The sad truth [that there aren’t many honest people in the world] seems to be true.
The bracketed clause is a content clause: it ...
The short answer is that it's ambiguous.
Interesting could be interpreted to modify both series and anime, or just series.
To be certain, you need to repeat interesting or rewrite the sentence.
We could watch a series or anime; both are interesting.
You have this correct:
We could watch an interesting series or anime.
This is the usual way to refer to a choice from the group of interesting things which are series or animes.
But it will be ambiguous if plural (so the article is absent) and will be understood on the sense of the particular adjectives and nouns:
Look at the big buses and taxis
First of all, I don't think this is a matter of "so" at all. It is essentially the issue of commas with coordinating conjunctions: FANBOYS.
Yes, when two independent clauses are connected with a conjunction, a comma is often used. This is not a strict rule, but a general guideline (note how I used a comma before 'but' even though it is not needed/...