Re: Switch to formula
The length of time it takes for milk to dry up is as individual as every women. I was still making milk 6 months after weaning. Will you still be leaking? I would guess unlikely but that is no guarantee either.
An idea, to cut down on your guilt, maybe you could keep one nursing session per day, like before bedtime. Once you are down to only one per day it is unlikely to cause engorgement or plugged duct issues when you go away for a few days. If it does, you can hand express into a sink for a couple minutes, no big time commitment. You might even be able to come back to the same once-per-day nursing schedule after the honeymoon, no pumping required.
I don't have any advice on slowly switching to formula, but since she is already taking bottles I think your idea to swap one more bottle per week is sound.
My little man was born 12/17/2010.
Baby girl was born 4/30/2014.