Not knowing what type of eaters will be at the event, I might increase the number of racks you're gong to cook, if you anticipate leftovers. If you're allowing the people to serve themselves, they may take three or four ribs at one shot.
As long as you have your costs covered and making a profit, you should be good to go. But that profit better satisfy you for future jobs witht the company. Do they know this is an "introductory" fee and it may go up in the future?
Be sure to write everything down that you used or spent money on. That way you can guage what your needs will be, costs are and how much of each item is needed. This will help you see how much profit you are actually making.
Diamond Plate FAT 50 Ultra
55-Gal Horizontal offset
2 55-Gal Vertical Barrels
Anything worth fighting for is worth fighting for dirty!