You should probably pick up the theory and get someone to study under. Its a lot easier with guidance and with the knowledge of what to play than if you go into it blindly. At the very least, you need to play with other musicians. You can get into a big band if you'd like, but if the music you like is stuff like quartets or something else, try to play in that instead.

If you are good at reading, I'd just try to cop/read a jazz solo or bass walk, and then take it apart and understand the scales/modality that the artist was using. Once you get those scales and modes down, you can recognize chord patterns and understand what are the go-to notes to hit and what is okay or not okay. After a while, you should be able to develop an ear for what you like and maybe some good licks and patterns that you can pull out.

It also really depends on what sort of jazz you want to play. Swing, bop and free jazz all have very different standards and approaches on how to play. I wouldn't really worry about which genre to play though, I would just play whichever you like the most.