I do banjo strings one at a time and I mark the head with a light pencil mark at the bridge if I have to take them all off.

I use Moon Bridges on both of my banjos. They're canted forward and radiused which makes them very stable. They're also compensated and a day after install there was a marked improvement in tone, it really opened up the sound. Mileage may vary as a buddy of mine installed one and didn't notice much difference in the sound but liked the improved intonation.