So, I finished up all the wire connections, pushed everything into an empty saber body, and fired up my first stab at a DIY.
In short, it worked. This thrills me, because it tells me that my wiring diagrams and the document I made that shows what goes into each splice point were correct.
But, internally, it was also uglier than Palpatine's imperial buttocks. A lot of lessons learned, that I should have made note of from examining sabers already on hand. No biggie, the wiring can stay as it is (I can shorten the excess AV switch wires easily, and the only time the LED wires will need careful replacement into the hilt will be when I go to change MLS units (set up with QDs), which won't be all that often. The rest is a matter of removing electrical tape and doing some work with epoxy or something similar.
But...it worked.

Oh, my son was also very, very excited that I just built a saber. I guess I'll have to get more DIY bits for his first sound saber, because it's cooler if dad builds it.