AMRO can be as big as the amount of food that can be cooked in the largest pot in the stwst, which is around 100/115 portions.
Actually, to have a good AMRO, some less participants should be included in the program.
Food team needs at least 3 or 4 people.
Don't underestimate trasportation. During the festival a car is needed mostly for food logistics.
Food logistics:
AMRO is organized with a system of private stay and some other accommodation modalities.