The game is incredible. You'll hate Tiburon even more if you get into NHL and see how much awesome they put into the game. By no means is it flawless, but it's quality level is just fantastic.
Anyways,
1) I don't know if there will be a 1v1 league. I thought about running one, don't know if I'll have time to though. They usually crumble. One of the biggest reasons why they don't work anymore is OTP/EASHL.
Online Team Play (being introduced in Madden this year, alraedy in FIFA) is the strength of the game. Nothing beats 12 human players on the ice, it's a fresh game every time and should be even better with the new physics this year! But yeah, there is a league, it's just called the EA Sports Hockey League (EASHL) where you play as whoever you create (yourself, some weird looking mofo, whatever) and find a team or just play pickup games with randoms.
2) There isn't much of a league experience in-game (still have unannounced modes for this year tho, Online Dynasty is speculated). Think of Madden's League mode prior to Online Franchise. NHL 10 pretty much has that with a couple extra features built in. It's not really used as the EASHL is where it's at for online play.
One other note to add since it seems you want league play. Unlike Madden, the AI in NHL will give you a good time. There's plenty of sliders (that actually work) to customize it to your liking and playing offline can be plenty of fun (the dynasty mode is fucking awesome too)
Any other Q's?