Re: More cast than mics, RF gain structure...
Dick's advice is spot-on. As far as level-setting goes, most inexperienced actors would strain to give you a usable level, let alone clip a portion of the signal chain without yelling at the top of their lungs.
My SOP for settings gain structure for theatre mics is:
1. Get placement right (this includes picking elements with the correct sensitivity, etc.)
2*. Set transmitter gain/sensitivity (have actor go through loudest lines as if actually on-stage - I have them shout/yell if that's what they're going to be doing during the performance)
* - If swapping TX packs, I find that setting the gain to the loudest variable usually works fine; just don't give that TC to the quietest talker.
3. Set channel gain "accordingly", so that there's 3dB-6dB more headroom during rehearsal than during run-of-show (most performers, whether they realize it or not, perform louder during the show than at practice...fine by me, as long as I compensate for it beforehand).
4. Monitor repeatedly as needed during rehearsals and adjust if necessary.
