Normally it takes an age for me to formulate and out a plan of action down for a project, however this one has fallen into place rather quickly!

Today I have put in place my prototyping board:

An Asus Tinkerboard w/Justboom Amp/DAC hat

Arduino Mega w/lcdshield (plus a wifi shield underneath. No plans on using it in this project).

Two potentiometers.

This little setup will allow me to test everything from getting data from the (currently hypothetical) slide mechanism using the pots, start work on formulating the serial data to be sent to the Pi from the Arduino for notes, work on using the lcdshield and buttons as a method of menu control to the Pi/Tinkerboard, and also work on how the Pi will handle that data.

I also had a little play with Fluidsynth on my laptop (an aged beast running the Pi x86 Desktop OS) and it took me ten minutes to get all dependencies installed and notes coming out via python script.  Great start so far!!