Yes.
If the account preexists role queue, it estimates your rank in the various roles from a few months worth of pre-role queue data. When you play as a given role it only affects the MMR from that role.
Yes.
If the account preexists role queue, it estimates your rank in the various roles from a few months worth of pre-role queue data. When you play as a given role it only affects the MMR from that role.