I recently did pulled pork for about 160 people. I was able to fit 6 8lb butts in my UDS and it took about 14 hours to get them all to 200 degrees. We ended up with about 1 butt worth of meat leftover (we also served grilled chicken thighs and someone else provided the side dishes).
My advice, is to get everything in writing...even if it is a gift and you are not charging for the service. Have everything detailed out. Everything. The last thing you want is to run out of food, especially for a wedding.
Once you have it all in writing, be realistic about it and say no if you have to.