depends on the team you are playing and also depends whether silverware are more important to you or being financial sound seasons after seasons
At level 5 you should be able to identify "title contenders" after the first 2-5 games, generally this is how i set my winning bonus
position 1-4 - max bonus
position 5-6 - 75% - max bonus
position 7-8 - 50%
position 9-13 - 25% - no bonus
Obviously some league will have many teams with very close quality so you have to be the judge.
That is assumed you are able to play the game everyday and set it based on your opponent.
But bear in mind League isn't where you make your cash in game, it's CL. try to get to at least SF of every CL and you should have enough cash to buy fast trainer every season