Yeah the ban email specifying exploitation of game economy is fairly clear.

Multiboxing is not a shield behind which you can protect yourself from the rules of the game. They didn't ban you for multiboxing.

RMT is RMT whether you're doing it with 1 toon or 5, and whether your 5 toons are on one account or 5 accounts, and whether your 5 toons are on a different account than your main account which can also get banned, and whether they linked your 5 accounts to your other 5 accounts, and so on.

Seems fairly common in these kind of threads. We can't help you with your RMT accounts.