Main Panel Power
#1
Main Panel Power
Would it be wise to turn the main breaker off in the main panel if I am adding a new breaker? Not sure if it is adviseable to insert it while hot.

#2
It surely can't hurt. The only downfall is having to reset your digital clocks. The upside of shutting off the main breaker is that the bus bars downstream are safe if you should bump it accidently with your hand (always remember that the utility side of the main will remain energized).