Max A Team Defending Training
Here is a training plan for a team playing 4-5-1 and 4-4-2 for league games and 5-4-1 for friendlies. The idea is to maximize the number of a-teamers who are receiving training.
4 defender trainees.
1 winger who plays in defence in friendlies and so is also a trainee to become a nice balanced wingback. 19-20yo and as much wing as you can afford.
4 IMers who also train defence in friendlies.
1 winger who is old and cheap.
2 forwards who are old and cheap.
This gives you the flexibility to play all permutations of 4-5-1 and 4-4-2 in competitive matches, with any amount of F, W, and WTM you like. It also keeps your outlay low as your non-defence players are also trainees during the friendlies, and means you don't have many players hanging around not training and not accumulating value (only 3 A teamer outfielders are non training). And you still have the full complement of 9 trainees!
Note this regime increases the chance of injuries to your IM players as they play twice each week, which is why they need to be young so they heal fast!