A couple of things:
1. Everybody will have different opinions on how to run a team. This is by no means the only way. It is exactly what I said it was. Just a quick guide for those who have no idea what they should be doing.
2. Should you have 3 18-19 y.o.? sure, but getting other kind of young players (20-23yo) will help the efficiency of your training. One on One for example is two position training. It's not hard to get 5 players 48 minutes in 3 games. Why train 3 when you can train 5? Especially with a new roster devoid of real talent. With 5 you can sell some players eventually and still keep some players.
3. The sooner you expand your arena (and really the sooner you can get it to 8-9k capacity) the better. Math people. The sooner you expand, the sooner you make more money. It takes a week to expand, and in that week you can find trainees and a trainer.
4. Ya'll should really leave this chat open to new player questions, vice filling it with nit-picky, complex, philosophical management philosophies. It will just make new players MORE confused.