Another test to try: running reaper and the pedal software on one Pi with screen.
If both run without bottlenecking the CPU or RAM I can use jack to run the input to the effects, then into Reaper.
This will be, by far, the best setup if it works.
One Pi and screen to power, no need to run a network between devices and a local MIDI/OSC controller.
If testing works I may consider creating one enclosure for the screen and buttons of the controller in it.