The G10 has a very impressive spec, I also have a Canon HV20 tape based camcorder of 2005 vintage and still use it along with my HC-V700. Please check that the Canon will run for the time required before buying, the files on the SD card will be very big. This should not be a problem as long as the camera does not take it upon itself to switch off after a period of time thinking you have forgotten it!
Do use the supplied software to download the files from the SD card. It will sort out any additional "housekeeping" files created by the camera.
A remote mic will be essential as the sound captured by the camera at the back of the theatre will be rubbish! Full of echo and dampened by the seating etc.