Andy, how possible would it be to get a feed from your auditorium sound system? That would be the absolute best option for audio, in my opinion. Most sound systems should be able to provide you a line output you could connect directly to the camera. It may be an issue if all the audio inputs and outputs for the auditorium are at the front of the auditorium, however... that could be one long cable run.
As far as cameras, I don't have a specific recommendation off the top of my head, but I can poke around. A lot of cameras will use Quicktime in the web browser on Mac, which almost always introduces latency, and that could be a problem in a production. Don't want kids running out on stage four seconds late!
I use this sony mic with my axis q1755's.
but will work with alot of other axis cameras and its powered by the camera so you dont have to worry about the battery in it
With Axis cameras you might want to consider their new free software Streaming Assistant - Check out AXIS Streaming Assistant | Axis Communications