Conjunctions, commas, and multiple sentences

Since commas are used to represent a tone contour in speech, I heard every one of your commas. I would say they're just right; pretty much the way I'd say those sentences. Some of them remind me of the comma that I hear in a favorite punch line of mine:

• And, who knows? Maybe the horse will sing.

Without the comma it doesn't sound right. To me.

Comma rules have to do with intonation -- speech melody and rhythm -- and not really with grammar. Punctuation of any sort is a feature of printing technology, and not of language. One of the exceptions is the fact that non-restrictive relative clauses need comma intonation at the beginning, and also at the end if they're not final in the sentence.

But with short phrases you don't usually need commas, no matter what kind of syntax is involved. Unless, that is, you want to use them. Commas are always a matter of speaker's (not writer's, but speaker's) choice.