So I got the footage (of our rehearsal of act 1 scene 1) on to the computer and everything looks and sounds fine. The lack of preparation hurt it a little, there were lines of dialogue for which I had no usable shots as I hadn't planned my angles, I just filmed several takes of them acting out the whole scenes with me focusing on different elements each take. Very rough and ready. I made a quick edit to show the band and they like it. The acting was pretty good, and I can see where I need to be more careful and plan my shots better.
I switched the audio to manual control to film their song at the end, they played very loud and the camera handled it very well, the levels were set correctly. But the vocals were of a very poor quality, even though the rest of the instruments came across very nicely.
I'm filming a few bands this weekend live, and there doesn't seem to be much of a chance that there will be any separate audio recordings made, or even the opportunity to go through a mixing desk (as it is such a small venue they only put the vocals and the kick drum through the PA). Will have to do some reading and see what my options are.
Crowd noise is also going to be a problem if I can't get a microphone close to the bands....