Is the top donors setting in the donations settings page enabled?
It shouldn't be running still after it deletes the old database field but I will include a check for the field in the next update. In the meantime you can patch this by manually removing the core_queue database entry for the membersLegacyField background task. PM me with admin details if you need assistance.
Not currently sorry but more gateways are planned, no ETA yet.
Yep fully compatible with several bugs fixed at the same time in the latest update. I'll be doing another round of bug fixing updates again and then switch to new features after.