Regards to noisy Images. If you can use bounce flash that will help.
Honest advice is if you can only get a useable shot at max iso, then go max iso. A sharp in focus but grainy shot is worth a lot more than a blurred out of focus grainless shot.
Also explain this to the band, and/or their manager before hand, and explain that the quality of light on the stage will affect how the images turn out, this. Tamron 17-50 2.8 is a cracking lens if you could stretch to this, sharp and 2.8 throughout the zoom range.
Bounce flash, and stop your flash down a little if needed to avoid the obvious shot with flash look. Play about and experiment. Lastly enjoy it, I know you want to do your best, but making a boy band look perfect under a pub lighting setup without flash and a dose of luck would be a hard ask of many pro photographers, let alone an amateur.
Lastly shoot RAW! This gives you the easiest way to reduce some grain, and also sort exposure problems.
Lastly, Lastly. Good luck and make sure you post some results up!