It is hard to give any solid advice because we are not sure what lighting conditions you face in that event.

What I would say, based on my little experience:
1) It is likely you can use a lower ISO 1600
2) Get a fast zoom lens, I used 17-55 f2.8 or get a faster prime lens
3) Try not to use flash, it ruins the lighting the cheographer had in mind, and it irritates the performers and audience.
4) Shoot RAW, you might need to do some PP to recover lost details.
5) Scout the venue, find out where you can/need to stand and wherether your lens can cover the range.
6) Attend the rehersal, you can capture some good moments there, the lighting might be better, you can anticipate key moments during the actual day.
7) Have fun.