When I first started my team 32 seasons ago, I was determined to draft my own team
It worked for a while, but I realized that it was a costly crapshoot. Sometimes you get lucky and find really good players. Often you don't. Or you can get a high potential player who starts with low stats. And pay a lot of money in the process.
Buying trainees off the TL is much more effective. Depending on what I am training, I will look for certain attributes (like stamina or OD) and set a minimum for them. Then I look for potential. And I try to find players with similar builds.
I train for what I need. I think big men are easier to train, but guards are more important in the game. Right now, I am training guards for both teams.
This season I had 5 trainees for both teams. My regular team will have to sell 2 at the beginning of next season as I am about to start single position training. My Utopia team will train 5 until I feel there are 3 players worth training at one position.
As for potential, it depends on where you are. My US team was in a very competitive D3 group for a long while. I realized I was going to have to step up my talent level to progress. That's why I laid out some cash for HoF potential players this season.
My Utopia team just needs some guys. So PAS or Superstar players are fine. There will probably be a day when that changes
As far as what is valuable, who knows? I have sold players that I thought were average for very high prices, while players that I thought were better went for low prices. All it takes is for one drunk manager to fall in love with a player to make him valuable.
Training players is both rewarding and frustrating. But it's better than spending a ton of money on some injury-plagued, foul magnet.