hey, so you're right they only need to get 48+ as the requirement for full training so playing them anymore would not helpful for training purposes but is still a good idea for game shape. The general consensus is that playing the 3 players, that you want to train, a full game at that position, so that would mean all the minutes go to them and their name is in each slot at that position, is the best way to train players. Hope that made some sense and helped you out a bit.
BTW Morwood, I know I'm new to the league but I think it's awesome to keep things active. I've been in a bunch of leagues since I started playing and all of them have been practically dead, so it's nice to see things different here. I think it's a great idea for the charts, you could take ideas from the nba website on power rankings or different stats that we can't find already. I would love to help and in the past I would have but time constraints don't let put as much in to this game as I used to but I think it would be really cool if somehow you could make that happen. Good luck.