Hi M!

As a relative new-comer to linux-audio, I struggled with the same issues you're having.
I had intended to document my own learning of JACK MIDI, and have a repo online here
concerning exactly that. I just fixed the build errors, but unfortunatly there's only a very
basic example currently available: If you would like to add to it, please do :)
https://github.com/harryhaaren/JACK-MIDI-Examples

In a similar fashion there's another repo for general audio programming tutorials.
There's a bit more available there, but again maybe its a bit too basic for your needs.
https://github.com/harryhaaren/openAudioProgrammingTutorials

HTH, -Harry