Hello OperatorHesh
Your ideas are very good. If I may, I would like to share some of mine.
I don't think that you should be able to start and complete a transfer immediately like you can now, or at least there should be a setting that adjusts this option. I think it was 17 or 18 last time negotiations took some time, and other clubs could also be making offers. I would like to see a situation where you have to change and improve offers, bonuses, promises, or even complete other signings to help convince your target to join your club over another. Like bidding wars in real life. It makes it boring when you can come in last second on any deal and swoop the player with no resistance. Also, players should be more realistic and intelligent when it comes to squad roles. They should be able to determine by the squad you currently have how often they will likely get to play, and factor that into their decision.
Another thing, we know that all players aren't loyal, but most respect their former clubs and leave on decent terms. It would be a nice touch if your former player would refuse to celebrate scoring against you, bringing a level of realistic connection and respect to the game. It's not the biggest thing, but it would probably be well appreciated.
Also, in real life, players signing for clubs far away from or different from their nationality is often facilitated by a fellow countryman already there. This could be simulated and factored into the decision making of your transfer targets.
Youth players should be more realistic as well, not demanding senior contracts while they are nowhere near good enough. And if they leave your academy, they shouldn't disappear. Also, if you get great players in a scouting report, you would have a limited time to sign them before another club beats you to it.
That's all I have for now, I might come back with more.
All the best to you!