teensy-eurorack VS eurorack-awesome

also you can use an fpga as a great logic analyser. can decode all sorts of protocols. check papilio fpga, it’s the best cheapest logic analyser you could ever find. it’s been very handy, helped me build this thing (sounds a bit like what you’re trying do) https://github.com/newdigate/teensy-eurorack

https://github.com/newdigate/teensy-control-voltage or https://github.com/newdigate/teensy-eurorack perhaps?

For open source gerbers you can send off to get made there is lots of stuff out there. This is a big list on Github. I've built the nickajeglin analog logic module which is really good. Maasijam has some really good stuff as well.

There's a good list in Eurorack-awesome although many are analog designs.

if you’re okay with 0-5v cv there are lots of references like https://github.com/mattb/teensy-cv. more here https://github.com/newdigate/eurorack-awesome

A good place to start is sdiy and the legendary modwiggler forum modwiggler or github. github

With that background, if you're comfortable with schematics and doing pcb layouts, open-source modules can be the cheapest way to go. Here is a link with a bunch of github repos. Some have gerber files, you can send off to somewhere like JLCPCB to have the panels and PCBs made. Minimum order is 5 I think.

You can get a lot cheaper with some of the open source stuff out there. Here is a link with a lot of stuff. You'll have to source companies to do panels and pcbs.