oh hey that's me (juv).
some observations: I'm not sure if I just happened on the magic formula, but season plan: balanced, training focus: finishing (until it is capped, then balanced edit: with a striker obviously) , use all the staff you can afford, and always prioritizing playing time in your transfers seems to work pretty well. I can generally cap all my attributes in the high 90s before my player starts declining, especially with the "rough diamond" trait (though not necessarily get all the specialties). I don't know if "rough diamond" is doing that much, but from the description is certainly felt like the one to pick.
The relationships with family members etc. is interesting, but if it has an effect on player growth or performance, it's not very clear what the relationship is. I did get an interesting interaction with a player who hated me because I turned him in for match fixing while in the Saudi league but I don't know that it affected anything else other than being an interesting story.
Similarly with buying stuff that boosts morale, by the time your stats are up there, your morale is generally very high all the time anyways. I have a save where I've won the Ballon D'Or and am still in modest lifestyle because my morale is already 100. Maybe there somehow needs to be more of a reason to interact with that stuff?