If you start halfway through the season I don't think it's smart to spend a lot on trainees. They're much cheaper at the start of a season and they won't be missing weeks of training. I think starting with star/allstar trainees is good, you can try the first half season training secondaries, then the next first full season get some good trainees and start with the 2 position training (JS, RB and 1v1) so you can continue training the first trainees and the new ones together. After 1 and a half season I guess you can get the hang of training and sell the first trainees or keep them if they're useful backups.
Only half a season and quite some errors in minutes and the rest of training won't do any good for PAS or higher trainees. Better use your money on your arena first, practice with some cheap trainees and do it right in the first full season.