Cool, you've finalised it! I've been to Tallinn; Oslo & Stockholm from your list. I loved Tallinn; Stockholm was pretty cool....but I must say, I preferred Bergen in Norway, to Oslo...
Visa for Russia - I don't know personally, but I do know
BigRedTruck is American and goes to Russia regularly with work - I'd PM him, he doesn't frequent these parts very often these days, but he'll definitely reply to a mail.
Flight booking...I think you'll just have to keep checking back...not sure how far in advance they update schedules?