I have a few questions:
Are there going to be any side dishes?
Who is supplying side dishes?
If you are delivering the meat-who is setting up the serving table?
What size plates are being used?
I have been catering for over 20 years and see a few problems that might occur. I am not a smart ass or over critical---I would like you to be able to benefit from errors that I have experienced in the past.
This does not sound like a "Catering Job" it sounds like a "Meat Drop Off" job. There is nothing wrong with a "Meat Drop Off" job if that is what you want to do---but be aware of problems.
PROBLEM 1: side dishes are not sufficient for size of party because they pot lucked or had a friend do them or blah blah blah. If anything goes wrong with side dishes then "Nice Rack BBQ" gets badmouthed by all in attendance. People attending the party do not know who supplied what---but they see you and assume it is your fault. CURE FOR PROBLEM 1: When you cater---cater everything--side dishes are your friend and can save you money.
PROBLEM 2: Do not depend on anyone else to control your side dish supply. You are making sure there is enough meat---also make sure there is enough side dishes. Every ounce of beans or coleslaw etc that is consumed saves on meat supply.
PROBLEM 3: Setting up the food line is EXTREMELY important when it comes to catering. In a buffet line all food should be set up according to cost. The higher a food costs---the farther dwn the line you want it to be. I set out plates, silverware, napkins at the head of the table, then usually salad, bread, side dishes then chicken, then pork, and beef last. If meat is set first it becomes an "all you can eat carnivore delight" and you will loose portion control.
PROBLEM 4: Plate size and utensil size will control your serving size. If you have a 4 ounce ladle in your beans most people will eat 4 ounces. If you use Chinet heavy duty-3 compartment plates- the small compartments hold 4 ounces. Guess what-4 ounce ladle-4 ounce compartment--a very high percentage of folks get a four ounce portion. Never put bowls out next to the salad or beans----folks will grab the bowls and fill them with meat.
Now to the meat
I buy 1/2 pound untrimmed tri tip for each person. After trim and cook you will lose 25% or a little more. 1/2 pound equals 8 ounces raw per person--25% loss will put you at a 6ounce serving for each person.
Chicken leg and thigh quarters weigh one pound each---a ten pound bag has 10 pieces in it usually. When supplying three meats---a quarter chicken is too much for one serving. After cooking cut the legs and thighs apart from each other. A ten pound bag will give you 20 servings.
Pork will shrink more than the beef---but I still cook 1/2 pound pork for each person if it a 3 meat plate. Tri Tip is more popular than chiccken or pork.
PM me with any questions----we are here to help each other-----good luck