How much orzo should I make for 30 people?

The conventional serving per person of most pastas is 2 ounces uncooked, which would give you 60 ounces, or 3.75 pounds.

as part of a meal, on a plate with an entree, and a veg or salad?
if so, then 1/3-1/2 cup cooked orzo p.p. is plenty, so i'd do ~12 cups (cooked volume).