Reunions are the hardest small event to hold well, because the guest list is every age at once. Toddlers, teenagers and great-grandparents all need something different from the same afternoon, and a single room cannot give it to them.
Grounds solve it. Children go outside, the older generation stays seated indoors with the doors open, and the people in between move between the two. That is why this works here and does not work in a rented hall.
Practically
Five to six hours, daytime, usually a summer weekend. Food is almost always a buffet or a shared spread. Parking on site for the full count matters more than people expect, because reunions arrive in a great many separate cars.
If your family runs past two hundred, say so early — that is a size very few venues in the county can seat, and we can.