Dudes, I am UNIQUELY qualified to answer this question, because for a few years I had one customer and used a school bus converted to run on french fry grease to haul their freight. Later I wrote a college paper on the details of it - EO won't take it as an upload but PM me and I'll send it to you. It's quite a read and you'll learn something.
The short answer is NO and NO. No reputable carrier would take you on in such a vehicle. But the big problem is the bus itself. Most short and mid busses are on International 4300 chassis, the EXACT same as a billion box trucks so it isn't the weight capacity. Nor is it the height - the deck on most busses is 48" dock height or close enough. Nor is it the driveline - they get the same Cat C7s and 7.3L power strokes as anything else. Transmissions are almost all 5 and 6 speed Allisons, same as a box truck. But the ride, gearing (top speed/mileage), HVAC, handling would kill you in short order. On my bus, a 1993 International, there were 3 totally separate and independent braking systems, such that the brakes would always work....always. So in total, you could spend a lot of money and do a lot of work to make a bus into an expediter, but you'd be better off to either start with a box truck or just buy something already done.