In addition to what everyone else has said, the coach has to be able to communicate with the other coaches throughout the game and especially if there is a change in the match strategy. If there is no communication between coaches, that somewhat defeats the purpose of alliances.
As for amount of experience, it takes none. You gotta make sure that you keep your eyes on the field, though. That part of it is integral to how the match turns out. Also, make sure your driver or operator hears you when you're giving an order - sometimes they get caught up in the adrenaline of the match and do not hear what anyone is saying
Even though everyone should know the match rules and scoring inside out, the coach for sure should.
Good luck!