Where we live in Tennessee (well, our "permanent" residence, I guess), there's no building codes to worry about. So it'd be no problem to throw a few together and call it a house! To top it off, there's a company the next county over that has lots and lots of shipping containers; dunno what the price would be, but couldn't cost too much to have one delivered 30 miles away.
My plan was to put six in a square configuration. So you have the normal four making a square, then the ends are doubled up. One doubled-up side would have a large living room. The other side would have three bedrooms plus a small hallway. The top would be a kitchen, the bottom would have laundry area and a guest bedroom. You could walk all the way around in a loop (you'd have to walk through the guest bedroom, but it shouldn't be in constant use). You'd also have a nice private courtyard in the middle of the square, maybe even enough room for a small swingset. So feel free to let little kids go out and play, they can't wander off too far!
If I wanted an enclosed garage, I'd simply get another container and put it on the left (if I connected it to the rest of the house, that'd make it triple-wide on the left side). Should be pretty easy to convert a container into a garage. Would still have lots of room at the other end for junk...I mean storage of really important stuff.
For insulation, I'd want to insulate mostly on the outside, since space is a premium inside. I "might" put up some thin drywall on the inside just for looks. Electric lines may be run along the edge of the floor. If height isn't a problem, I could build a false floor, and run electric/water/etc. under that.
Who knows, if I ever get around to doing this, I might do things completely differently. I have given it some thought though, and have at least a rough idea of what I could do.