Sounds like a great way to get into the catering business. First, if you are going to do this, be legal. The few dollars you are going to make on this is not worth getting sued if someone gets sick and they blame you. Since it is a wedding, I would make sure you know what you are responsible for, ie., setting up a buffet line, serving from the buffet, clean up, emptying the trash. Also, weddings are typically late, be prepared to keep the food hot.
As for the quantity of food for 100 people:
62 pounds of raw pork(8 each 8 pound butts)
4 each #10 can of beans
10 pounds of fresh bagged coleslaw
You probably would be able to cook 8 butts on 2 UDS. As for as what to charge, I recommend taking your food costs x 3. Add in additional labor, and rentals. Hope this helps.