You should get a level 3, since you have 2 good training prospects. If you're willing to spend a couple thousand more, you can get a L3 trainer for 8.5K a week. (I pay 7.5K a week for mine!) If you can afford paying 10K, 12K a week for a L4 trainer, though, I would get one. You have a lot of young players.
P.S.: If you have to ask for help on the Help forums, how can we trust you as NT manager?