1. Check this blog and follow the links he gives.
Wow, thanks! Lots of useful stuff on Mari there and an interesting blog on the whole!
2. Of course you have to learn (to read) Russian! Trying to learn Mari without Russian is a bit like trying to learn Irish without any English.
Sounds like a walk in the park from you slavic natives.
Anyway, as I said, I'm not really serious about this right now and I have lots of other stuff going on, so learning Russian (or Mari, for that matter) is out of the question this year, but maybe I'll come back to it.
(By the way, I think you could learn quite a bit on Irish only knowing German, there are quite a few books on the market. But then again, Irish has that fairy tale popularity.