Yesterday I received the PCBs from @oshpark  (Thank you so much for promoting them to super-swift service and fast shipping!), and assembled them in the evening. They work perfectly, and I'm really happy with this design. The power switch and the connector for the battery are in the right place too.

I added a bunch of photos below in the "build instructions" section from the assembly process. I haven't decided yet whether I want to ship them completely soldered, or with the headers and the matrix separately — they are a bit fiddly to do right, so it will be nice to do them for the users, but then it makes it harder to ship them cheaply, and the exact headers you want depends on what kind of headers you have on your Feather board.

On the programming side, I updated the library to work with the new version, optimizing the display routine a little bit in the process, and also made the library disable the RGB status LED on those Feathers that have it. Your programs can enable it back, of course, and provide some ambient lighting.

I'm still thinking about the best way to write the tutorials for the games. I have decided on the first game in the series — a simple maze game. I also did some sketches for the accompanying illustrations. This is the part that I will need to focus on for the rest of the time left.