I wouldn't do over a 75 shot personally for nitrous. The cams aren't going to get you so much, stage 1s are mild AND if you don't do any other headwork or tuning (isn't really THAT neccesary on those cams, honestly)
Theres no reason to run a stage 1 crower LS cam if all youre looking for is the highest whp. You can run a stage 2 crower cam on stock valvetrain as long as you retain the stock redline, and make more power than the stage 1.
If you go with stage 2 crowers, your going to have to upgrade your valvesprings and retainers. Trust me on this one. Stage 1 your fine with a stock valve train.