I've started training like that too, 6 Star potential guys on 2 position training. It's a good way to start out and learn to manage minutes and it can certainly be worthwile, since I sold them for a good profit. I personally like focussing on 2/3 trainees and make them excellent instead of 6 good roleplayers, though both can be worthwhile.
As said, you can train 1v1 and JS until you make a decision, but I'd advise to keep your P. Allstar and your Superstar because they can become real good. Then keep the best Star potential guy (nr 2 or 3 I think) as 3rd trainee.