Some questions regarding the mechanics of training in FM20

[fraggert]

Apologies if this isn't the right place to post this.

Long time player here, I have some questions that I've always wondered about but never bothered finding out so here goes:

1. If I set my player's training as say a Mezzala for example, does that mean he will only work on attributes that are important (highlighted) for that role or will he only work on familiarity with the role/position? Or both?
2. If I set a player's individual training to Quickness for example, it will obviously increase the rate at which the player improves in pace and acceleration but my question is would it slow down progression in other attributes to focus on Quickness?

This question is more specific about the mentoring system since I skipped on FM19 which introduced the new mentoring/tutoring aspect of the game:

1. What is the best way to go about mentoring youth prospects? I have a youth prospect with fairly low determination and neutral/bad personality, I thought about promoting him to first team so I can mentor him and making him available for U18 so he gets game time but the problem with this is that at the start of my save I hired new staff with good "Working with youngsters" attribute for my U18 coaching team and I would like to keep the player in U18 so that he can benefit from the good youth coaches. Should I just suck it up and promote him and try to get some coaches with good "Working with youngsters" attribute for my first team instead?

Thanks in advance!