1. I am new at this, but the way I understand it your vision primarily is your level DIII etc...and inside of the level things like your success, your schools prestige, etc effect what you can see...you can't recruit what you can't see. People will say their vision sucks when the recruits aren't very good, or numbers you can see of a certain position.
2. When you do AC scouting trips he will tell you. If he says he's about reached his potential, that recruit isn't like to progress well. But if he says with your coaching this recruit could improve a lot...that's good.
3. Core stats are everything...because those core stats are the primary factors that govern how well a player is at a given position. All the overall is, is all the atributes added up...so take an OL his core stats suck but he's got an elusive rating that is off the charts...so his overall ends up high but who needs an OL thats elusive? I want him to get in the way not out of the way! So that OL wont be good at the position even though his overall is high. SOmething else you can do with those is change their position to one that is more inline with what stats are high for them.
Im new but I think I understand at least these Qs pretty well, so I hope it helps.