I bought 500 tokens and changed some of them to cash (around 11 millions) and bought 18-22 years old players 5 stars with 20+ quality from the transferlist. They will properly be 4 stars next season but wont it be possible to raise them again with just training them and how do i get 6-9 star players? Will it be possible at higher level to buy them from transfer or what?

I'm also working on my stadium and can i get players with the academy and how often and for what price?
Last thing is how i get the locked building on stadium unlocked so i can build them.