Welcome! Glad to have ya! I'm sure others will chime in with some other thoughts. This group is great like that...we all seem to have an opinion.
I think you're looking in the right direction. A full size truck chassis...something in the 47-54 passenger range. It seems that Missouri has a lot of buses in that size. I see you're in Kansas somewhere, that's why I add the Missouri bit. Our school district has a few of the 6-8 row variety as well. You certainly don't need a 65-66 or larger bus for your intended purpose! I would tend to try to find the biggest bus you can...you can always go smaller, but hard to make it bigger.
Something on a bread-van chassis, GM P-30 might work out well. It doesn't have the ground clearance that a full size truck chassis does.
There are lots of resources to check. A good one right here in Kansas is ks-bus.com. They are in Lawrence and really nice to deal with. I went to Ohio to buy my bus though from a private person!