It's maybe a bit early for me (experience < 1y, please pardon what might be a naive wall of text) to tackle these questions, but having a degree from another field, landing a job where people are passionate is going to be hard with my little experience.

Open-source projects seem like a great idea, especially for someone like myself who doesn't have many creative ideas, although I finally found one a few weeks ago (fullfilling my own needs as no website seem to do what I'm thinking of atm).

It's rather niche though, and I could probably do it on my own but I don't know what I could learn that would be useful. I would probably keep using the things I already know if no-one more experienced can suggest appropriate tools (kinda related to the top post about over-engineering).

My CS culture is not that great for the moment (working on it) so what should I learn ? Everything moves so fast. It's also related to your argument : how to find open source projects that might interest me and where I could be useful, as I don't even know them in the first place.

I also slowly discover what I would like to work on (mostly enjoying working with data/databases and also algorithms although I'm probably a bit weak there for the moment, but I really enjoyed doing google's hash code this year). Reading other people's experiences helps of course, but it's still difficult to find the right questions I should ask myself, so the answers are even less precise.