There is a CPU quota limit (and a disk limit) that you have to get approved to raise (and I think there's a limit to how many requests/second you can make to the GCE API), but if you get those approvals, you're good.
There's very little difference between the two (a few standard library differences at most + a little syntax). 3.4 (and Python 3 generally) is the future of Python. Learn it first and you'll be on good footing.
Docs are a good place to start. In the projects I've worked on, new contributors usually enter when they've found a bug/desired-feature and worked out a fix for themselves. Aside from that, good first commits are usually smaller, so it's easier to review, and address a single concern. After you get a commit accepted, you can start claiming commits.
Answering questions on Stack Overflow / mailing lists / issue trackers can be a good way to build up trust in your abilities and a working relationship with other contributors.
Often projects label things that are "good for a first commit" and you should check out those.
All that said, most projects are eager to include new people, and personally I enjoy helping new contributors feel comfortable and get their commits accepted.
Do something exciting for you. More than anything, employers want to see you get excited and energized about something. So if there's some really cool problem that you want to work on and you create/help maintain an open source project related to it - that's great. Or make your own app. Whatever: it doesn't really matter, it just matters that you're into it.
If you don't have that much $$, get a Macbook Air. I did all my development on a 13" Macbook Air before my current job (and I still use it in my personal time) - I love how light it is and easy to carry around. If you're doing iOS + Rails you don't need any fancy power to do the majority of your work (and if you do, go buy time on AWS or something).