PCBs are incredibly cheap to print (<$25 shipped for me to print at https://jlcpcb.com, IIRC), and he shows you how to do some mods to the schematic using KiCad [1].
BV also has some crazier minimal keyboard designs like this 18-key split one with lots of layers: https://www.youtube.com/watch?v=yNOGEtqn85o
[0]: https://www.youtube.com/watch?v=JqpBKuEVinw [1]: https://www.kicad.org/
It's ultimately the same process I used to create my Analog Hall Effect Keyboard that was reviewed by Chyrosran22 recently: https://youtu.be/iv6Rh8UNWlI
https://wiki.ai03.com/books/pcb-design/page/pcb-guide-part-1...
Once you build your first little macropad, and verify that your design is generally correct, you can fork the repo you created and pretty much copy/paste your MCU region, and build a new grid of keys around it. The guide also gave me good tips on what to have assembled, and what to hand-solder, to be able to cut some costs.