everything you see here was purchased for a grand total of $120. no programming required. some soldering necessary.
observation: 4 expression pedals is probably still not enough expression pedals.
the opendeck software is robust and mature. it now has the ability to compensate for pedals which don’t go all the way down or up.
This device is definitely “waiting” for MG3. With the new MIDI controller concept it is so much fun to play around with parameters one would never have thought about before (at least I didn’t). It’s so easy, and with visual feedback, to hook up pedals and switches. Each single, controllable parameter a VST contains is listed up. Pedals and switches can be connected to various different parameters simultaneously, switches can be momentary or latched or inverted just with a mouse click.
You and your Pi board will like it!!
Let me know if you can think of any more (useful) pedalling modes 
