If I remember correctly then the PDA notices are from your assistant head coach (I think that's why he has a 'development' rating).
I wouldn't advise training only one player during a season. It's best to train players who you want to keep for a longer period. I usually train one player for 2 weeks, then train someone else for 2 weeks. If you don't train a player then his ratings might drop after the season. J.R Smith lost his highflyer ability after one season because I focused on his offense and defense and not athletics.
When training always focus on the area where the player is the weakest. Dwight Howard for example is a power player and an inside stopper so you want to focus on offense (who knows, he might develop a killer mid-range jumper in a few years

) but don't forget defense and athletics.