Hey guys. I just stumbled across this thread and even though it seems to be more hardware oriented so far, I'll try and contribute.
Regarding Euro Rack, the way I learned is fooling around with VCV Rack. It's a virtual euro rack system that's almost free. That is, there are modules that aren't free but there's no reason you couldn't learn everything on the free modules.
There are tons of YouTube videos on learning and using it but here's an overview.