Amazon has given the OP the reason for banning: his account was linked to a previously banned account. Numerous emails to CS and one to the executive team have confirmed that they saw wrongdoing and that the ban was warranted.
As for the OP's books disappearing from his Kindle, perhaps it wasn't deregistered prior to him attempting to access his archive (I assume this to be the case, otherwise he would have had to register before "clicking the archived books line" which resulted in the deletion). I think that books will be removed from a Kindle which is linked to a banned account.
As for having multiple accounts, it is wise to have separate seller and buyer accounts. Since feedback is open for all to check, sellers just may not want potential buyers to see what they themselves have been buying
, but of course the accounts should never interact with each other.