Today was finally the day. I assembled the main board. After all of that, I hooked up a 12vdc power supply to the "a" power input, and the screen came alive with my test outputs. I found a couple of glitches during assembly, and I've done enough projects to know there could be more waiting for me as I start wiring up peripherals, but it felt pretty good seeing features instead of smoke.
Here's a picture of the assembled board (except for the display, which slides into those blue sockets on the ends; some barbarian let the soldering iron touch the shorter one).
More details in the build instructions.