Hi Debbie,
YOu can get my e-mail address from Betsy. I'd be happy to help you with this but don't have much time at the moment. Tomorrow I can give you some more info. You'd be surprised how little you need. I cook for huge groups all the time. Figure out your needs for 5 or 10 people and then multiply it. YOu won't need any more than that! Figure that more people eat burgers than hotdogs, unless you have children. Depending on th size of the burgers and what else you are serrving (which is a VERY important factor) I owuld guess 1 1/2 burgers per person and 1 hot dog. YOu should be able to get 5 o 6 slices of tomato aout of a medium one. And 10 to 12 slices of onion out of a medium one. Everybody won't want to use tomato and/or onion (especially onion at a gathering). I've done this bbq thing for 220 and had sooooo much left over. That was 3 years ago.. I would do it very differently now. Write me here or get my e-mail form Betsy. Ihope this is helpful information. Good Luck.