1/22/2016 Once you’ve announced either activated ability, it’s too late for anyone to interrupt you by trying to remove the creature you sacrifice.
1/22/2016 Once you’ve legally activated the last ability, it doesn’t matter what happens to your life total.
1/22/2016 Your starting life total is the life total you began the game with. For most two-player formats, this is 20. For Two-Headed Giant, it’s the life total your team started with, usually 30. In Commander games, your starting life total is 40.