It's the shrinkage that fouls things up. For pork butts you'll normally get 40% or so shrinkage - that's why I recommend 90-100# of raw pork to get about 54-60 pounds of finished meat - you may do better since some butts don't shrink up as much.
The beef is the same problem depending on the cut and how lean it is. Packer briskets will shrink about 40-50% too.
On the slaw, I'm with Jeff in that I'd buy the preshredded at Sam's or another restaurant supply place. The 3# bags at Sam's yield about 16 servings each.
I did pork and sides for 450 over the weekend. I cooked about 280 pounds of raw pork, 18 cans of beans, and I don't remember how much slaw (I bought too much). We were able to feed everyone, sell some quarts (at least 60 or so), and provide a full counter pan of pork and fixin's to the fire department. There was still some meat left. I left it there for the staff to lunch on this week!
Providing the "only" meat for an event is different from providing "an additional meat" - you sure don't want to run out until after everyone has had at least one serving!!
Southern Brethren BBQ Competition Team
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KingFisher Gator Rotisserie cooker, WSM, Stainless 5 burner with IR gas grill, Turkey Fryer, Weber JD Commemorative grill, slightly used Bandera chamber for future use as a cold smoker, Masterbuilt 40" insulated ELECTRIC smoker