Denis998, I prob will skip this one. I'd do a single-season league, but I'm already in a couple long-term leagues already. So don't count on me to fill one of the slots.
Long-term leagues are a commitment. I think a lot of them end up puttering out... which can be a bummer if you spend all your time strategizing "for the future" and then the next year everyone is like "Meh that was boring/I hate my team" and bail. Hah. So make sure you guys are really committed to keeping this going for the long-term.
I'd recommend you guys do it as H2H points league (where each week teams face off against each other and the teams with best records advance to the playoffs)
I think GC's Yahoo! H2H League is probably run that way. A couple leagues here already run through Yahoo. You could do this one through ESPN to be different. I think their scoring system is based on the NBA Efficiency stat (we use to call them Birdies after Larry Bird)... Just a simple equation: Points + Rebounds + Assists + Steals + Blocks... subtract missed shots and turnovers = the fantasy points the player puts up that night.
But you guys can define your own scoring multipliers. Some people like to add multipliers that favor assists or steals, for instance. This is where a lot of fantasy leagues can fail, though. I've seen people quit just because they don't like the way the scoring system works. And you can't really change the scoring system after season 1, because then it has the potential to screw over someone who built their roster based on the original scoring system.
All things to think about when building out a long-term league you expect to participate in for the next decade