Yes
it is a direct debit to your bank account only.
You can pay by credit only if you pay once or you can pay x amount but they will still debit your acct. as normal until the dues are paid in full
Yes but you need to give MS time to set it up for you so don't wait until too late in the year to try to switch it over. Since you are already paid up for this year, you can set this up any time now so that everything is in place for next January.