Working away at it. I carved the edges of the timbers with a #11 X-Acto, and gave them a wood texture by dragging a wire brush across the insulation foam. I sanded a 45-degree bevel into the edges of several parts and did a test fitting.
Figured out the base plate. It is a piece of plastic with four holes drilled into it. Screws will go up and into the corner supports. I did this because I was concerned about the piece blowing away in the wind, and this way, you can take off the base plate, add a bag of gravel or sand, then screw the base plate back on. Why don't I just include the weight in the finished piece? Because I have to ship it, and there's no point adding extra weight before it's needed. (Note to self -- I need to buy some stainless steel or brass screws for this.)
Cut out the windows with a long X-Acto knife. I lowered the side windows from the attic to the second floor because I realized the insulation would be likely to break near the roof line. With thinner material, as in the original papercraft model or my foamcore prototype, it's not going to snap, but I didn't want to risk it with the insulation. If I make this building again, I'll likely add a small window on each side for the attic.
Painted the plaster areas with latex exterior paint. After this, I painted the beams with a dark brown acrylic.
Added a transitional color between the beams and the plaster, because it just didn't look quite right otherwise. I may add a wash of that orange color to age the plaster, particularly down at the bottom edge of the building. The beams still need to be dry-brushed with a light color, but everything is coming together nicely.