bleenisgrue
sure.
midi is a protocol that allows up to 16 channels (good old serial midi) on one "line".
limitations of midi are resolution (a standard midi cc message only has 128 different values, and speed. midi works at 31250 baudrate, hence a message takes roughly 1ms to be sent.
the resolution thing can be overcome by packing a value into two cc messages, giving you a 14bit value, which should be plenty of resolution.
boolean should not be a problem (use note on and note off for example).
trigger, the same note on and note off.
the questions are:
-how many different messages do you want to send to each arduino?
-do you mind the small latency of (serial) MIDI?
as for the midi connection itself i see two options:
1) use a usb to serial midi converter and connect the serial midi out to all arduinos, probably you want to build a small midi splitter. i used this schematic once, and it worked great:
https://moroccodave.com/2017/10/04/diy-midi-thru-box-version-2/
or you buy one.
2) program the arduinos in such a way that they represent themselves as usb-midi devices when connected to a pc (or BELA). that way you buy a usb-hub and simply plug-in all arduinos into the host port of BELA. depending on the arduino this reprogramming is easier or harder, but it should work on most arduino boards.
while this method is "easier" on paper and also faster (usb midi is faster then serial) there is no electrical insulation between bela and the arduinos and hence it could introduce noise as you observed when you only used BELA to drive the plugs. with serial midi you have an optocoupler in the serial line, that should take care of all noises.
