Invest anything you can in training.
Investments in training include reasonable trainees, optimised training slots and coach. If in doubt about best affordable quality of (existing) trainees better upgrade them. Any compromise in trainees/training will cost a lot of money and performance.
Normally the same for coach, but we see a change in the staff-system, so no valid advice at the moment.
Any other investment has a slower (and lower) return. Postpone it. Seriously.