20lbs is only 40 8oz whole breasts or 80 half breasts. If you have the time and a large enough flatop I'd just do them on the flatop. If not, sear them, put them on a sheet pan, and finish it in the oven. Chill quickly.
It all depends everybody does it different i believe it all depends on the freshness of your poultry normally i don't wash the raw chicken first but i go through about 80# a day so i recieve it everyday fresh. Some chefs like to wash poultry first i guess to give them a better peice of mind or perhaps to just have a product that doesn't get any bitterness taste from any blood that might be on it.
Ultimatley i believe the decision is yours.