Sounds like a cool bus. We'll need to see some pictures!
On hills the transmission should pick the gear it wants. It should be ok parked on one dual. I wouldn't drive it anywhere.
It shouldn't be kneeling when you stop. Maybe when you apply the parking brake.
I would jack it up and block it on the axle. Make sure you are on level ground and the other wheels are chocked, you don't want it rolling off the blocks. If you are working off concrete heavy duty jack stands rated for the weight of your rear axle would be best. If your working off gravel or dirt go with cribbing. Make sure the wood is in good condition with no splitting. DO NOT USE CONCRETE BLOCKS. Here are some guidelines I found.
Cribbing For Heavy Vehicle Lifting – First Due Tackle
DO NOT GO UNDER THE VEHICLE WHEN THE AIR SUSPENSION IS INFLATED. IF IT FAILS YOU COULD BE CRUSHED!
Be safe and have fun.