Welcome to the Class B Forum wilburleft - I'm glad that you like it.
I have a few more photos here: More Photos
You've probably seen them.
I don't know much about the 2007's. I haven't read any complaints from current Sprinter owners about lack of power.
Re: 22 gal grey/black combined, & 21 gal fresh - I think my wife & I could go three days with that. We drink bottled water though. I doubt we'd be able to get 6 showers but you can get clean enough with a wash cloth........
Re: propane gen. 45 lb tank - cooking & fridge doesn't seem to use much propane. You can get a few meals out of a 1lb tank. I think the generator could consume 1/2 gallon per hour running the airconditioner. It consumes .6 gallons per hour at full load.
The continental spare tire kit is a standard feature so there might not be room under the sofa. Just a guess on my part.
The towing tongue weight is 500 lbs. so maybe both the spare tire kit and a small motorcycle can hang on the hitch.