With todays modern tech its not that tough. The biggest issue is making sure every thing is on its own frequency and the frequencies are properly spaced. Shure makes a software tool for their mic units that will tell you what channels to use based on how many units you plan to run to make sure they are properly spaced. You can find it here
One you have chosen your channels its more about setting up your mixer as you best see fit. With the digital stuff thats out there now assigning mix groups to manage everyone is not that hard.
Another approach I used to use to avoid overlap (when budget was tight) was to use mic units that were in different spectrums. This usually involved using some of the older stuff which was susceptible to outside interference although I never had any serious issues with it. By doing so you avoid any possible frequency overlap.
The traditional approach to wireless has always been one channel one mic but as it gets better and faster and most importantly cheaper, I would not be surprised if they start to phase in the technology they use in todays cell networks (TDMA, CDMA, FDMA) allowing multiple units per channel, frequency or time spectrum. This would allow more mics than people you can fit on the stage.