Hey Excal...
Go for it!
(or not)
I've got a '76 chinook and can help a little. Mine was a $400 project so it doesn't have all of the pieces. It does not have a heater, but I have heard that some do. I am considering the possibility of running a small space heater off of the deep cell, but don't know about that yet. I also don't have the table so I can't say how it folds down, but I believe it would make into a full size bed. The space up above could hold a small child; my concern would be him/her falling out (would need a rail or something). As far as the front seat arrangement... I don't know.
I might get yelled at a little here, but the five lug doesn't seem to be a problem with these vehicle as long as you don't over load it.
Mine fits me just fine and I like it really well. Four people seems a little tight (even with one of them an infant), but what the heck, fun is fun.
You might check Craigslist and fly the family down to Seattle if you find something interesting, and drive everybody back home in comfort and style. (Okay, that might get a little pricey, but you would build a memory that would stay with everyone forever... and that's not a bad thing:)