For shooting with the ambient stage lighting, crank the ISO up a bit, to at least 1,000 or 1,250,or maybe higher. Keep in mind that with stage lighting, there is often a HUGE disparity between the light on the singer/actors and the background of the stage or set...often the backgrounds are quite dark, darned near black, and the talent is lighted up pretty well with a spot light, or a fairly narrow type of flood...this causes the camera's in-built exposure metering to give suggested exposures that are often eight, ten, or even 12 stops OVER-EXPOSED for the talent, at least when using shorter focal length lenses like 28,35,50mm. So, be aware that the light meter's suggested readings will often be wayyyyyy off. If you are using a telephoto lens, like say your 105mm macro, and the subject is pretty large within the frame, then the chances of the light meter giving the right ballpark exposure go way, way up.
You need to keep in mind that it's better to get a noisy shot with good clear focus and motion stopped, than it is to come back with low-noise, but perfectly smeared, blurry,jerky,smeary shots made at ISO 200.
When shooting with the 28 or 50mm lenses from closer distances, if you are going to use an automated light metering setting, you might think about setting the exposure compensation to Minus 5.0 stops, if the subject is spot-lighted, and the stage is mostly dark....and even then, you might still be washing out the subjects. SO, maybe you'd want to go with manual metering, and set the camera at say ISO 1600, f/2.8 at 1/125 second, and if that's bright enough, stay there;;;if they switch on a brighter spot, click the shutter up to 1/200 or 1/250.
IF there is a decent line of sight, shooting from 15-25 rows back with a fast telephoto like a 105mm f/2.8 offers you the ability to maintain pretty easy focusing across the width of the stage.