Well you're 21 year old is your highest paid player, go to your economy page and see how far over the salary floor you are. Do a cost/benefit analysis, if you are near the floor you don't really make any more weekly money by selling him, plus he helps you win games so you can make more in attendance money.
Your hall of famer is 6'6" (I'm gonna say his stats look more inside SFish just guessing) so without knowing his stats you might wanna train his guard skills first and then his inside skills depending on the type of player you want, if you train his guard skills up for a season or two, your other two younger (cheaper) players will still benefit as well and over the course of training your HOFer's guard skills you will most likely fix that one player's handling skill.
Also I would ask your NT if your HOF player is on their watch list, you may not even bother caring about the other ones if they give you an idea of the type of player they are looking for.
Just some ideas.