Here is a dry fit of the main wall and floor pieces; they fit together pretty well, sort of like a puzzle:

I put all the light fixtures in about the place where I will want 'em, to figure out how to string the wires:

The lights even work! The bulbs on the second and third floors will be for fireplaces, and the bulb lying in the middle of the third floor will be put up in the attic:

Even Mister Blinky down in the kitchen (there is a squirrelly connection somewhere):

My plan is to attach those extensions to the back of the trim pieces that go along the second and third floors. I'll make some sort of screen to hide that terminal block...