Not silly at all, but, no. AC means that the positive and negative reverse, so to speak, at however many cycles per minute, so the machine does it for you.
The AC balance would be the other way round if you swapped workpiece and torch connections e.g. if you were using say 70% balance one way round you
would have to dial up 30% the other way round to get the same effect.
For just about everything TIG, yes.(Not sure how this applies to stick, though.) For ease of reference (it could even be that the machine will auto sort the balance) I'd keep it -ive torch, +ive earth. That way, when you decide to do a bit of DC, it'll be right.