If your number of guests adds up to more than 150, which is the maximum that the Barn can hold comfortably, then you still have a few options.
American Party Time carries a variety of tents that work on the property to allow you to have up to 250ish guests (you will need additional parking for this many guests). Below are diagrams of the possibilities you have for larger guest amounts.
You can also choose to have your tent in the grass by the ceremony site. The buffet would be in the lower level of the Barn so the main floor is open for dessert and dancing the night away.