The highest player I got was an 8 star. Think I got him free from KOH. I found it extremely difficult to train him any further but since he was a standout performer and an attacker, he sustained himself quite well for 2 Seasons I think by getting MOMs. Even so i didn’t bother trying to train him as he was too old.
I really do not think it is possible to maintain a full 9 star team with the free greens we get. Has to be a tanker or token buyer.