Never heard of a bus going through weigh stations, is that a non-southeast thing? I drove a MCI-8/9 coachs in the past and some Bluebirds.
Yes you'll need at least a Class B CDL. A passenger endorsement would be a good idea too, untill the buses are converted. Those buses are not great runners when they're cheap, really check them close and have an "expert" on hand to inspect. Thats a long trip, if you go transit, a slow trip probably. Watch the age too, make sure you can still get parts for the brake systems, cooling, etc.
What model of bus are you planning on?