You started in the right place with music theory. As for learning synths, you can do it in two ways - just start using them, fiddling and playing (whether its a software synth or hardware synth) or you learning actually the fundamentals by books, video and articles like these: https://www.soundonsound.com/series/synth-secrets-sound-soun...

I started the first way in the early 80s and did the second and have a life long love of synths ( I don't even know how many I have now but probably around 30-40 hardware synths, samplers and drum machines).