Anyone ever got banned for that?

ive done 200b over the last few months not had any issues, i think if you buy all from 1 guy you might have problems, i try to buy a few bill from a few different people

how do you trade it, get sent isk directly or through a contract?

Both

I hear if you create a contract with some worthless but unusual items that are not for sale in the marketplace (e.g. mission items with 0 isk value) it is less likely to draw attention. But on paper, yes, all trading using non-eve resources is considered real-money trading and a bannable offense.

Yes, you can.