3. You don't need a desalinization "plant" onboard, really. Or at least one that would use fuel at all- just make a Solar still. Of course it would be a bit slower but you could either (a) make a large array of these in one corner of the barge or (b) just scale up one/a chain of these floating ones and tow the still/stills behind the barge.
5. "weld them together"? Yeesh. Have you ever seen one of these in person? You could EASILY support 50+, maybe 100 or more people on one of these.
I figure anything that saves on fuel is a good thing- you'd need positively massive amounts of diesel just to get anywhere. One thing being tested on oil tankers and other cargo ships is a setup of giant kites to help propel the boat. Kind of like a scaled-up version of the ones used for kite surfing. But again, steering is going to be a problem. The paddlewheels would definitely help (assuming you can change direction independently both port/starboard), but even modern barges with thrusters and such need tugs to help them maneuver.I hadn't thought of solar stills, but you would still have salt as a by-product, which as I said, isn't a bad thing.
I was actually thinking of starting with a smaller barge to start off with. Easier to acquire and set up. I couldn't imagine more than 30-40 people living comfortably off one. When you factor in food and water, and the creation thereof, space becomes a luxury.
Then again, I'm imagining more of a hedonist, semi-anarchic, "Harm none, do as thou will" kind of thing.