You will have nine players who will want to play every game. Once you know who they are, after they complain about not being used after your first game, use them 90% of the time. Use the other players in cups and loan a few of them, but check your team after every game. When selling players, sell them. Do not release them, because the team cracks up. If players need a break for just one game more than more game off, they will complain.
To find out how to unlock specific players, go to "Track Record" and press R1 until you reach the screen that informs you how to do so. With the specified league titles and cups to unlock the desired players.
In February, players that don't want to renew contracts are free. Go to advanced search and enter 1 to 1 for the number of years left on contract. The players that show up on the search result are free agents.