Right on, shooting a band with flash can be tough.. so for that I'd recommending buying/renting/borrowing an f/1.4 prime lens. That way you can get some good shots with just the light on stage. The lens you have currently will push your ISO to silly places, if you're even able to get a shot at all.
For walking around and shooting people though, I'll hold my flash in my left hand and the camera in my right. That way you can get some creative lighting angles, and you don't have that head-on look to everything. If you have a neutral colored surface near you (wall, ceiling, big assistant with a white t-shirt), you can bounce the flash off it to soften the light as well. Since nightclubs are usually dimly lit, the white balance is usually warm compared to the flash. So if you can gel your flash with a CTO or 1/2 CTO that would be ideal. (smalls gels can be had cheap or free, since they're often promo items)
I think even with a fast prime, there may still only be enough light on stage to get ambient light shots. You'll probably still need the flash if you're walking around elsewhere getting people shots.