Keejse,
Very interesting idea. Not sure how hard hotel is on the engine, the ATR seems to do alright, is a lot lighter than an APU.
Some of the problems with it in the ATR sense are you can not refuel with hotel running. It is limited to only 10kts tailwind, and dependent on wind direction we have to turn the bleed off to stop the exhaust gas being sucked in.
If you do go with the apu, something that you can leave running unattended would be great. As I understand most props with apu's require someone on the flightdeck or at the least in the cabin as they don't have automatic fire extinguisher capabilities. I stand to be corrected.
Have you dug around for info on the ATR 92 concept that is on the drawing boards at ATR at the moment. The Q400X is another one in concept at the moment. I personally think the ATR concept is better as it will be a clean sheet design, with a gear design similiar to yours.
I agree with a earlier comment about crosswinds, the problem with the ATR is the wing continues to fly to around 40-50kts, spoilers that dump lift on landing would start to solve some of the issues surrounding the interesting crosswind handling techniques.
Look forward to more concept ideas.
Cheers