other questions are, how are you being paid, do you want leftovers? Per person or per event? The ribs and butts are not cheap any more. 2 butts using slider bun, 6-8 racks will give everyone 2 bones each. You can count chicken pieces. This is a lot of meat you are serving, so people might be inclined to take more ribs than the other two. I would make sure your client knows the limits on the ribs. Another thing to do would be to cut the ribs into single bones. Figure 4 oz of side per person. That would give you 200 oz of 50 people. That translates into 6.25 quarts. You will have leftovers of the sides. Not knowing the demographics of the group, this is just my best guess.