Sounds like you have your work cut out for you Cedars.
To put the size in perspective....a Suburban is pretty close to 20ft so that bus is not really all that huge. It's wide and it's tall and makes you think it's a lot longer then it is.
Sounds like you have some good ideas of how you want things. Just put some thought ot safety aspects. You probably want to add some seating with Belts for passengers. Might look around and see if some RV captains chairs with seat belts pop up.
Heating and cooling is going to be the trick. Put some thought to upgrading the insulation. Limiting air leaks would also go a long way.
Is this a slab side like a school bus or it is more of a fancy bus like they use as airport shuttles?
If it's like a school bus then it's quite easy to remove windows and cover over the holes. Not bad to cover the complete ise where the windows go and convert to a RV style windo like you would find in a Motor home. Take a litte of the "Short Bus" look out of it and get the windows where you want them.
Cooling is the easy part since you want to carry the generator on the bus. Just throw a roof mount on it. Heat strip might be enough if it's insulated well. If not there are heaters available that will make heat using the coolant from the engine. Down side is if you go that route then you will need suplemental heat for when it's parked.
Here is the site about the heater set up I was talking about.
That is just so slick for use on anything with a motor. That would give you heat in the cabin and pre warn the engine if the bus is a deisel and could be used for hot water if you ever decide to plumb the bus. Now this guy is into gagets so he has made it a little more complcated then it as to be but the timer is a nice feature especially if you use this to preheat the engine.
As for the generator. Put a acess door on the side into your storage compartment in the rear. Build a box to seal it off from the rest of the coach. Quick connects so you can pull it out as needed. Just need to incorperate a slide to get it out. Fair warning, Generator big enough to run the A/C and some other interior stuff is going to be around 125lb for a light one.