Graduation parties are usually held in a garage and a garden, and they usually run out of both. The problem is not the number of people — it is that they arrive across four hours rather than at a start time, so the room has to hold everybody who might overlap rather than everybody invited.
An open-house format wants indoor and outdoor space at once, shade, a food table people can return to, and parking that does not fill a neighbour's street. All four are why this works better here than at home.
Timing
May and June are the season, and the good dates go in February. If several families are graduating together, a shared party splits the cost and doubles the guest list into a room that can take it — which is a genuinely common booking here and worth asking about.
Four to five hours, early afternoon into the evening, with the grounds open. Ohio in June does what it likes, so having the hall behind you is the whole point.