Thanks for the kind words, I really enjoy having it there, I've used it quite a few times already!
To answer your questions ...
1. It holds about 2 1/2 to 3 gallons, I've filled it using a five gallon jerry can and it takes a little more than half.
2. I fill it before hand, and will generally fill it before any type of trip
3. Shrader valves (tire stems) can be picked up at any auto parts store, the size just depends on the drill bit you're going to use on the plastic pipe to create the hole for it!
4. I have onboard air now, but before that, I've used a regular hand pump from my mountain bike or a cheap 12v compressor I picked up at target for ten bucks. ..both worked just fine.
5. I get about two minutes of actual running water per fill up, plenty to take a nice camp shower, or wash dishes after cooking.
As for heating, purely solar...although I've considered winter needs and simply heating some water over a campfire and then adding that to the system would surely work on those colder months.
The trickiest part of creating this is sealing the joints and then drilling the holes the right size for the fittings. As for the filler hole, I had to get the right size washer to maintain a tight seal and keep the unit pressurized.
Hope this helps, if you think of anything else, just ask away!