I know this jump from hobbyist to professional developer is a tough gap to jump. As Karl mentioned, you are more than welcome at Hacker Hours
- lots of other attendees in the same boat, or who have successfully made the transition. Programs like Hacker School
have the added benefit of drawing in potential employers at the end of their session, though it sounds like you may be a bit beyond some of the beginner-oriented programs.
In terms of getting involved in an open-source project, I think it's a great idea. A good place to start is the gems/projects you use, are excited about, and/or have ideas for how to improve. Another piece of advice I like is to pick a non-profit to volunteer your dev skills for. That way, you get to build up a portfolio without time or money pressure from the "client" but will be helpful for them, and build up your portfolio at the same time.
Lastly, I've collected some resources for aspiring junior developers:
Hope those help!