Hmm . . . where to start? How about with a disclaimer:
This project is cost prohibitive for most people and even with the kind budget necessary for HDI rigid-flex having blind vias, it doesn't begin to compare to the creativity and sophistication exhibited by many of the projects on hackaday.io. If there is a takeaway to be had here, it's one part process mixed with a dash of layout.
Add moxy to taste.
Looking back at this project, I'm still pretty proud of what was accomplished in two weeks, even though there's plenty to cringe at. My only regret is not being able to share the firmware for . . . reasons.