I'm currently working on a similar project, using the Teensy 3.6. I'm planning on 4 swell shoes (3 expression, 1 crescendo) and the 35 or so pistons in my current setup. For future use, I'm setting up the wiring to allow for 128 buttons, and possibly the keying for the pedalboard. It should also be able to handle a 16x2 display for the stepper frames. Parts are actually working, but not yet installed in the console. I'd be glad to share the code (once I know it's reliable) and the wiring. Naturally, none of the examples (MANY are included at the teensy site) do exactly what I want, so the programming is proving VERY interesting!.
The buttons were originally wired to the Behringer UMX610 keyboards, but it was not reliable. After the existing pistons are working with the teensy, I'll be adding toe studs, and then a new name-board with the stepper control buttons on it. No project is ever really finished, is it.
This is a photo of the console from a few years ago, from an old thread.
Rick