I understand your question but this is essentially an impossible question to answer with hard numbers because the light intensity can vary so much. If you have a photography tutor this is exactly the kind of question they should be able to deal with as they can be on site to experience the settings with you.
If this is a significant event as you suggest, I would honestly suggest working with an experienced photographer, rather than disappoint all of those who want to photos by working alone and not delivering. At least attend the rehearsals and try out the settings you end up with so that you can make adjustments for the final live event.
Since light intensity drops of as an inverse square of the distance to the source, you want to be as close to the stage as the Field of View (what the camera can 'see'), so you want a pretty wide angle lens, and preferably one that can gather a lot of light: a 'fast' lens. You are looking for f/stops to be as low as possible - e.g. f/1.8, f/2, f/2.8. I suspect you will be shooting with a kit lens, which is usually the EF-S 18-55 f/3.5-5.6 IS lens: which is somewhat slower. If you can get a faster lens that would be helpful. If you are static and able to do so, then use a tripod to cut down on blur from camera movement, but you will still need a shutter speed that does not result in a lot of subject movement blur. Even with the aperture wide open and a relatively slow (but not too slow) shutter speed, you will likely have to compensate with a higher ISO. In that case I would set the ISO at Auto trialed with a maximum value of 4000 and see how it performs. If it does not need that higher value it will use a lower one. Finally, if you get noise, see if you can access a noise reduction software such as de Vinci De Noise.
Sensors in APS-C (Crop) sensor bodies such as the one you have, tend to be noisy, so I suggest you shoot in RAW and add a bit of exposure compensation (trial at the rehearsals will help here). Shooting in RAW will give you a lot more latitude to modify in post-production. You want the bright spots to be not quite blown to white.
Again, I will suggest you refer to others in your location - if you don't have a tutor, talk to folks who are experienced in photography. Perhaps talk to others who may have shot a similar event at the same site or look a the library of images taken there. This needs some preliminary research and work. Despite being (as you admit) a novice at photography, you have found yourself in the role that a professional would normally occupy in that you are delivering results for a client (paid or not) that will have expectations. One rule in that situation is that one should never learn at the expense of those who depend on your results.
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
