my setup

i am using some peripherals for getting data around my studio

• ESI M8Uex 16 din plug usb 3.2 midi interface, bus powered with data forwarding ports
• Expert sleepers ES-8, ES-3 and ES-6 for 10 inputs and 16 outputs of CV signals or full resolution audio
• Behringer UMC 1820 rack mount line level and ADAT audio interface with midi i/o
• IK UAI Powered USB 3.0 Hub
• Several usb midi synths

they all work simultaneously.  in order to use the 2 audio interfaces together in the same DAW i need to aggregate them in qjackctl so they look like one interface to any software accessing the jack driver.  

The expert sleepers provide audio or full bandwidth cv control interchangeably from all outputs.  This can be a mix of streams intended to control any cv based module including audio rate, lfo and envelope and even tweaks by hand.

midi input can be used to effect cv output through a mechanism you set up in a cv generating plugin such as cardinal or even directly from track automation envelopes (inside reaper that is).  you can also use cv as an input instead of midi.  you can record it as audio or a sample even, then re-use it for any section of the song.  cut it up and paste it just like audio.  or make a patch of several samples of cv modulation and re trigger them as you wish!  get as deep as you wish.  even use audio plugins on cv streams.

Im under the impression that most class compliant USB peripherals will work with raspberry pi.  all my synths that are usb midi show up automatically when i plug them in my 7 port powered hub.  there is a limit but i forgot what it is honestly.

i have not noticed any slop or sync issues when testing.  Im pretty sure reaper does active compensation for most i/o and plugins and such.  it may bother you but i dont really detect it but then ive not gotten the microscope out yet. 

A Roland UM-1 will work in a pinch and also handle system exclusive messages.