If this is going to be at night, I'd say your 50mm is going to be your primary lens. IS isn't going to help slow down fast motion. F4-5.6 may be usable if the stage lighting is very bright, but I wouldn't count on it.
My personal advice is to make sure you are at a fast enough shutter speed to stop the motion, regardless of how high you have to turn up the ISO. The reason I say that is the fact that I prefer a sharp noisy image to a blurred clean one. So if there is a compromise to make, I'd error on the sharp/fast shutter side.
There really isn't a rule of thumb with stage lighting. It can be all over the place as I experienced last night (
gallery here). I'd work on using center-weighted or spot metering as well. Evaluative will work when the lighting is even. However, if spots are involved (and often are) you'll end up with blown out subjects. For this reason, you may have to slightly underexpose your images.
Shoot RAW, you'll need it to recover some missed exposures and often to critically color correct. Some people use AWB or Indoor (Incandescent / 3200k) WB settings. I typically AWB and just color correct in post...But that too can be tricky. Canon bodies will often try and blow out the red channel, so that is something to watch. Luckily, in RAW, typically you can recover from small mistakes.
Good luck! Hope this helps a little.