Thanks for your 2 answers.
I am not a tokens buyer and I want to have fun with my team by trying to make my players progressing and keep them as long as possible. What exactly do you mean by power training?

Also, my intention is to compete for titles but not every year, not a problem for me if I stay 2 years at same level. So I would try to have players with 2 positions and a special skill to have a funny and variable tactics. Do you have any advices for me to maximize the performance of my team?