Hey Syed! Welcome, and thanks for wanting to contribute!
On the process - For smaller things, you can honestly just go ahead and open a PR - no need to "claim" it first. That said, dropping a quick comment like "I'll take a look at this" is totally fine too and helps avoid duplicate work. For larger/more complex changes, it's worth commenting first to discuss the approach before diving in.
On finding what to work on - Honestly, the best contributions tend to come from your own experience using the tool. You mentioned you use promptfoo a lot for testing before releases - what's annoying? What's a papercut you hit regularly? What feature do you wish existed? Those kinds of improvements are often more valuable than picking a random issue off a list, and you're already the domain expert on your own workflow.
On the Python/TS thing - Totally fine! A lot of the codebase is pretty readable if you're coming from Python. And some great contributions are things like docs improvements, adding examples, or small fixes where you don't need deep TS expertise.
Feel free to ping here if you want to bounce ideas around - happy to help point you in the right direction. And once you get a PR merged, DM me and I'll send some swag as a thank you!