Tattoo convention

I was asked to be the photographer for the Cleveland Tattoo Expo this year(woo!) and am on the fence on a few things. Figured I'd ask you guys that may have some experience with that type of stuff. The venue is the typical convention center with HUGE ceilings and pretty hit or miss lighting. I plan on shooting with a flash. What would be an ideal setup for flash? Diffuser and straight on? Bounce card? Mini soft box? Also, I'll be using a 17-40 f4L and am going to be borrowing another. Thinking a 70-200 just to make things a bit easier. Any recommendations? I would have most lenses as an option so recommend me something. Any suggestions/tips/help you guys could offer would be fantastic. Also, I get paid in a free tattoo! What should I get?