I'm attaching the mic plot from when I did Les Mis. We had 16 mics but it's the same situation. I listed the main characters by character name and the smaller soloists by actor name. The main issue is to make sure that if people are sharing mics you factor in enough time for the trade. Remind them that after they finish with their mic the FIRST thing they do, BEFORE changing costumes, BEFORE getting a drink of water, is to take off their mic and return it to whatever central location you choose to do the trades in. That's the other thing--don't have actors just hand mics off to each other. They should check them in and out with a sound crew member and do all mic trades in that location. It will save actors randomly leaving mics in unusual places.