your question makes apparent that you KNOW to have possible reasons for warnings OR ban why don't you try to invest a few hours in reading Google TOS and simple comply to the TOS precisely as published. Hence just be a clean and honest publisher and you have nothing at all to fear or worry.
Depends on how many site are in your account and how much each is making. If you have three sites, each making around $100 a day, then you would get a warning and maybe the site in question will be banned (not the account). However, if you have one site, and it is in question and you have fifty others making nothing, then chances you entire account will be banned. Peace,
If it is a minor TOS violation, you may (or may not) get a warning. If you try to cheat them, there will be no warnings...100% ban. I have got a warning once - that was a long time back. (The problem was with the traffic source). I still have my account.
Sometimes you will just realize that you are violating TOS, it doesn't mean that I know what I am doing is wrong, that's why i'm asking. This question is for the sake of all beginners in adsense.