How Much Chicken And Beef Should I Buy To Make Tacos For 100 People?

I am planning a taco lunch for the high school band. We plan to serve a choice of shredded chicken or ground beef tacos with all the usual toppings, rice, beans, chips and salsa. How much chicken and how much beef would you suggest I buy to make these? And why do you suggest that amount? Need answers ASAP as I start cooking tomorrow.