It took a few weeks, but the new boards are finally here!
I tried adding thermal vias throughout the board, but it seems the soldermask covered them. I'm not sure if that's better than leaving the vias open, but my guess is it'll at least prevent solder from the through-hole components from being wicked through the board.
The first order of business is to solder the through-hole components, run some tests and ensure they work as designed.
If all goes well, I'll put the kits up for sale on Tindie.
Afterwards i'll (finally) upload schematics and gerbers etc to GitHub.