I would agree with the suggestions of all the previous posters on how to arrive at raw/cooked quantities.
My only question is how are you serving the brisket? When you say, "or because it's whole, does it not stretch as far?", I am assuming that you are planning to serve the brisket SLICED. We serve ALL of our brisket PULLED. This makes it much easier to gauge the serving size and allows for less waste.
Morning Wood's post, " I would let your friend determine that ratio after you tell him/her the cost for each", is exactly how our contracts are written. We provide all of the technical data, such as suggested serving sizes per person based on the overall mix of food items, and let the customer tell us how much of each they want. This puts the accountability of running short/over on quantities on them and not you.
