If I leave autopay turned on, but use a top up card to prepay for one
month of service (or more), does it surrender my autopay reward (such as
bonus data and $2 discount) for the months covered by the top up?
You need your account to be active to be able to transfer your number,
so you would have to pay for another month of service in this case.
There is no other way to do this and you should not be leaving your
email on a public forum.