Introduction
Rico's Leyden Jar has been selected
Note: this post will be updated. As such it shall be considered work in progress. A change log is shown at the end.
Last change 2025.01.01 (yyyy.mm.dd)
The controller is considered priority 0, being 0 the highest priority.
At the time of posting this text, a very valid controller is available: Rico's Leyden Jar
As Rico himself states, it is a "xwhatsit controller in steroids"

QMK and Vial firmware are available. Modifications to the code will be required to ensure the layout and, in the future additions as the (priority 4) OLED display.
Constraints
- Interface to the PCB
- Physical integration - case
- LEDs and/or OLED decision to be taken
- Built-in/integrated controlled - impacts the controller and the case. It may increase cost as the controller requires 4 layer PCB while the sensing PCB can used 2
Spoiler: