If it were me, I would focus less on correct ISO and shutter speed and more on the story and the framing. What do you want your shots to say? It won't make a big difference at the end if your ISO was a multiple of 160 or not. Don't be afraid to break the rules, you may well have to in order to get the shot. A slower shutter speed will let in a lot more light, and, if the scenes don't have much movement, you'll never be able to tell 1/30th from 1/50th. On the other hand, shooting at 1/60th or 1/100th will accentuate motion, which is a cool look for dancing/sports/etc.
Also, you could bring a light along, which will do wonders. Have fun