I figure 3 people per rack of ribs. So, if you just plan on adults eating ribs, that equals 15 racks. I'd cook more. Since you have all of the other stuff, you could get away with figuring only 2 bones per person. That equals 6 people/slab. Your number is good for adults only.
A 9lb butt will yield about 5lbs of cooked meat. Figure 1/4lb per person. That's 40 people. I'd cook 2 more.
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