What we do is we have a 12 team league, and you keep 5. You can keep any 5, and there are no 'contracts'. So you can keep a player as long as you want.
We lock down Free agent pickups and trading when the last week of our regular season starts. So the team you end with there is your final roster until after our Championship game.
You have open trading, but no free agent pickups until the Super Bowl. At that time we turn in our list of 5 protected players.
There is still open trading throughout the summer until the draft, but no free agent pickups.
We then typically draft the end of July or early August, before the preseason starts, just to make it a bit more difficult.
Has worked out well in the past, and we have just finished our 10th season.
I am not the commish, but was for about 3 years. We kinda switch it around every few years. I think we have had 3-4 commissioners so far.