I played in league games on the Wass poker forum which is now defunct, for several years. We played on Carbon and then when Wass Poker opened we played there. It was called The Bragging Rights league.
Teams could have unlimited members - But only, I think 5 players could actually play per game.
1 game Sat and 1 game Sun.
Points were given out to the top 20 finishers in each game, more pts the closer you were to 1st.
At the end of the month...the team with the most points won a private game for real money paid for by the forum.
Teams were started by their captains originally and then voted in or out after that, month to month.
The captains had final say on who was in or out of the team.

I was a captain for a couple months, it was a demanding job in terms of organizing who was going to play every weekend etc. For example in the case of no shows right before the game, you have to have standins. And then if you have plans as the captain you have to have someone capable of doing all the organizing for you etc.

"Team play" is different then regular play. You chip dump to your team mates early on in the game when they are low, but not as much in the later part of the game. Some teams used Instant Messaging between player at the same table, telling each other what they were holding. This helps decide who is going to play the hand as most of the time you don't want your own players in the same pot together.

Can't think of anything else helpful at the moment...I'm sure more will come to me. We had a lot of fun playing together!