I think training different skills all around would amount to more money then just training jump shot. I would suggest Getting players with average or respectable in Jump shot, Outside Defense, and Driving and okay on the rest of the guard skills. Then train switching between JS and OD until those are both around the Prominent, Prolific Range and then using the rest of the training weeks left on driving and then you have a bunch of trainees looking like this.
Jump Shot: prominent-prolific Jump Range: mediocre
Outside Def.: prominent-prolific Handling: mediocre
Driving: strong-proficient Passing: medicocre
This is probably best case scenario but I think a player like that would sell for more then a player you are suggesting which would look like this.
Jump Shot: wondrous Jump Range: strong
Outside Def.: average Handling: average
Driving: medicore Passing: average
I agree with your idea of a lot of trainees but 6 is 1 to many, I would say 5 is a better number because then he could sell 3 for a good profit and keep two to continue to train, while adding 1 more 18 year old so he could 1 position train. Then he could train handling, passing, and jump range up while continuing a little bit on the other skills and he could end up with after another season 2 20 year olds looking like htis
Jump Shot: sensational Jump Range: strong
Outside Def.: sensational Handling: proficient
Driving: proficient Passing: strong
Again, best case scenario as far as training goes. he would need a level 4-5 trainer, but those would be some beast 20 year olds.