To cook gumbo for 20 people How much chicken and sausage would you need?

It is really going to depend on the recipe and how thick you want your broth to be.

One recipe for a chicken and sausage gumbo I've seen by Paula Dean, you would need 12.5 cups of oil (after browning the chicken) an additional 6.25 cups of butter and 25 cups flour to make the roux for gumbo to serve 50 people.