I do like how people claim to answer these questions without actually knowing the answers. One person in specific, in this case. Anyways:
1. Yes. I infract people for bumping old threads in the Market all the time. Also, if you "buy" an item from an extremely inactive thread, I won't get your stuff back.
2. Depends. If you've got legitimate backing for it, you're fine. Otherwise, shaky ground.
3. More likely a warning, possibly an infraction. Irrelevant questions should be asked via PM.
4. It's a very real possibility. In all likelihood, you'd just get a verbal warning, but an infraction is entirely possible.
5. If you're all-out flaming someone, then a ban or infraction is highly likely. If you toss in an obscenity or two to emphasize a point, it's probably fine.