Here are a few more possibly useful details…
The BOM is apparently missing references to the specific chips we used for the ATMEGA328P and MAX7219CNG, but reportedly these parts will work:
https://www.digikey.ca/product-detail/en/microchip-technology/ATMEGA328P-PU/ATMEGA328P-PU-ND/1914589
https://www.digikey.ca/product-detail/en/maxim-integrated/MAX7219CNG/MAX7219CNG-ND/948191
Another comment we received was that the RJ11 parts are nearly impossible to obtain without buying hundreds, so a possible workaround was to solder directly to the pads and connect up the LEDs and a current limiting resistor.
We’ll continue to post more details as they come in!