Count on 10-12 bones per slab. Chix, just decide on the pieces you want to cook and what you expect each customer to consume, this goes for the ribs too.
Iffin it were me, I'd do 7 racks and chix thighs and breast (1 chix per). Of course you have discussed this with the client or have experienced them before. YMMV
Peace and Smoke,
My Weapons: Custom rig - Kandi, UDS; Bubba Keg; 22.5 WSM x 2; 18.5 WSM; BWS extended party; BWS Gator and an Onyx Oven; 29' ft Coachmen Leprechaun (Lola).
Dan Chambers get well soon, so we can tell you to "Shut up Chambers"