Players you can sell: Vorm, Kyle Walker, Fazio, Rose, Wimmer, Son, Mason, Carroll, Chadli..
These are the players you need to upgrade on.. maybe take a season to judge, or you could do that right at the start and get enough money to buy better quality.
You'll need a back up GK, go for Donnarumma. He is good enough to start, but use him in cup games etc, and he wont let you down. Also in 3 years he will be HG at the club. Don't approach to sign as he often doesn't entertain that, instead offer Milan about $5m straight for him.
Timo Horn has an approx $9m release clause, tremendous keeper. If nothing else, buy and sell him later for profit.
Riechedly Bazoer can play at CB, DM, CM.. I bought him for $23m in the second season i guess.. get him earlier if he's cheaper.. quality player.
Dragovic has great stats for a defender, and iirc, no real weaknesses. Has a $28m release clause iirc, can be sold for much higher later on, though you won't need to do that any time soon, and not high on wages.
Mammana, Mere, Oxford are future super stars.
Laporte- release clause $54m is the finest CB in game imo..
For LB, the best available option is Ricardo Rodriguez if he's willing to come. Has a release clause that is a bargain given his quality. High wages, but deservedly so.
Other realistic LB options would be Jorge, Criscito, Matthew Targett, Jonas Hector, Jetro Willems, Achraf Lazaar, Arana..
You definitely need a better right back. Look at Mayke, Mario Fernandes (CSKA), Tin Jedvaj(slightly injury prone, but amazing.. costs approx $20-25m 1st season, fee being spread out), Bartra, Florenzi is amazing, but cant see him joining, Vrsaljko(realistic and perfect), Johnny(name? at Celta iirc)..
For CM, Tielemans is great later in the game, but is pretty injury prone and costs a lot. Something i learned too late.
Koke is a beast. High release clause close to $60m i guess.. That's still cheap considering i broke the bank and all my game ethics in terms of spending to sign him for $117m- his release clause in the second season.
Keep an eye on Hojbjerg and Kovacic.
Cubas is a good young player, Ilkay Gundogan is tremendous, and iirc has a decent release clause which is definitely a bargain, Joao Moutinho is great, so is Renato Sanches (get him if his release clause is $40-50m or under), Lucas Romero, Ruben Neves- he would cost over $100m on my save now in the 3rd year, and it's way easier to buy him at the start, no brainer!
Embolo, Barbosa, Leroy Sane, Vietto, Lincoln, Matheus Pereira, Bilal Ould Chikh, Andrija Zivkovic, Berardi, Icardi, Aboubakar, Asensio, Odegaard(just snap him up for his release clause)!