Amount of players.

[Corona]

That is a good idea. Like a real club you have a youth squad.

You say after 5 competative matches you get the opportunity to sign him starting the next season, i Think this part is a bit useless unless you are a token buyer.
Afteral, a season when you promote, means a star loss of a player. So lets say you have a 4 star youth player, it will become 3 star, and take lots of training (greenpacks, redpacks) to make him a 4 star player again, I think, most people go for at least 4-5 star players in their squad.

I was thinking of this:
Every now and then you get 2 youthplayers from your acadamy. 1 good player you can buy with tokens, and one bad player usually 2 star. If it is doable, You can have the opportunity to put both youth players in the youthsquad with a max of 15 without you have to sign them until they reach the age of 20. Then you have to decide to sign or release them. You can also just put your 2 star youth player there. Then at least your 2 star player has a bit of value instead of just selling it.