Why do you try to buy 4 stars players? When you can buy old 5 stars players kinda easy with 1 token ... you just need to watch a bid the auction list and you can find.
But I prefer young ones. They can pick up skill points easily.
Overall in my squad, I will start to sell once they hit 28/ 29 y.o
Season 14 - Level 14
League Champions: Season 3/4/7/8/10/11
Cup Winners: Season 3/4/6/9/10
Champions League Winners: Season 2/4/6