Start contributing to open source

I want to start contributing to open source. I aim at ruby, with or
without rails.

1) What is the best way to find the right project? Github?
2) Is it better to work on something that has just started with
development, or perhaps to submit patches for bigger projects?
3) What is the process like? If I like the project and want to
contribute to, am I supposed to message the main developer first?
4) Do developers usually accept help?
5) Am I better off sticking with one project or contributing to many
different ones?
6) Is it OK to ask the main developer questions about the project (both
spec and implementation)?
7) Is it OK to ask the main developer questions about ruby/rails (or I
should stick to forums)?
8) My free time varies a lot. Sometimes I have a lot of it, while
sometimes I am very busy. Does contributing sporadically present a
problem?
9) I like pair programming. Since I don't have anybody to work with me
at the moment, would it be a good idea to find another RoR developer
online and work with him/her, help each other out and comment each
other's code? If that sounds good to you, let me know.
10) And do you guys have any interesting project you need help with?

Regards,
Milan Dobrota
http://milandobrota.com

It's going to be tough to answer your whole list of questions, because
open source projects vary so widely, as do their contributors. As a
rule of thumb, I've found most projects are more than willing to
accept help if you show them you can actually improve things.

One option for getting involved over the short term: this weekend is
the Rails/RailsBridge BugMash, which can give you a taste of helping
out with the Rails source code. Details are at
http://wiki.railsbridge.org/projects/railsbridge/wiki/BugMash