Andrew Huang has a really good intro video on modular synthesis: https://www.youtube.com/watch?v=cWslSTTkiFU

Warning that modular synths are typically not cheap. However, most of the physical standalone synths that exist today use the same principles.

Physical hardware can be really fun if you don't end up going with VCV rack or syntorial as mentioned in this thread.

Good pieces of hardware for a n00b:

- arturia microfreak

- korg minilogue

- any of the korg volca lines