My thoughts on vending....for what its worth.
Take the 1% figure and plan for that, if you sell out, your ahead of the game. You haven't lost anything.
If it goes fast, refigure your numbers for the next day.
No large pit? What are you cooking on?
May be better off pre cooking and warming on site instead of a clusterfark of cookers, trying to keep temps, serving, etc, etc.
Good luck and get some pics!