Do you have to close your Traditional IRA after you transfer it to a Roth IRA with a Backdoor Roth? Or can I just leave it open with $0 left in it, so I can repeat it next year?
Most places let you keep the traditional IRA open after conversion, you can call for details. Sometimes you write it on the paper forms, other times there's an option on an online form.
With Vanguard I leave my traditional IRAs open with a 0 balance.