Leave the master at 0db. After processing each individual tracks/group tracks, make sure all of them are at like -18db-ish or lower, and adjust as needed. I keep my kick at -12db, and my snare at -15db, cus I want those to be the loudest. Whenever I do this, I find that my headroom on the master is exactly -6db or lower, which is a nice amount of headroom for mastering!
Yep, that's what I do on Ableton