Advice / Tips on photographing Masquerade Ball

Hi, I hav an opportunity to photograph a masquerade ball this weekend and as I am only in the early stages of my course I would greatly appreciate some advice / hints on how I can prepare for this great opportunity. I’ve been taking photos for a while now as a hobby but nothing too serious – photography is my passion and I hope one day to make a career of it. I have a canon 7d + 430 exII speedflash + 50mm 1.8, 15-85mm, 55-250mm lens. Which lens’ / equip would be most beneficial to take. I am gathering it will be in a function hall – dark with lights and i hav been told there will also be a rough backdrop up for posed pics too. What modes to use etc Some advice to help me prepare would be great. Nervous but excited as this is the first public / function I have done since starting the course. All in the aide of experience and practice. Really appreciate your feedback. Thanks so much.