Doubt much insulation...shuttle vans usually only run the heat while the engine is running, so they can put out max heat the entire time with no loss of efficiency plus the doors open every few minutes...no real advantage in insulating.
For an RV, burning propane, you don't want the heater running 100% of the time. I presume the bus heater is running off the engine coolant, which wouldn't be practical when parked for the night. For it to do much, you need the engine to get up to operating temperatures, so if you test it by starting the truck and idling for a couple minutes, no it won't put out much heat.
If it's an existing air/con, I presume it is powered by the trucks 12v system as a shuttle van wouldn't be hooked up to alternating current power under normal conditions (possibly an engine mounted compressor but I doubt it). You would need to rig up a battery bank with a large charger to provide a continuous supply of power to the air/con.
Most shuttle buses I've seen are not designed for under floor storage. I'm sure it can be done but likely major surgery will be involved.
If you are converting because you like to do projects, sounds fun. If you think you will save money over buying a class C, walk away now.
