What is your goal this season? If it's triple crown then you can do the following:
Scout all your opponents. If they are relatively close to your team's quality then you can invest greens in AMs, ST, MIDs.
Even if you dropped team quality before the season started then also investing in players will drastically increase your chances of treble.

If you want a decent season with some silverware(2nd /3rd in any competition) then save up rest for next season.

Your training level is mediocre ATM. You are just starting so it will grow gradually. Don't worry about it. Just keep training your players daily.
It's obviously better to have more drills unlocked but you need not worry about it. Just one advice regarding this - when you level up you get an option of upgrading drills and unlocking new one. At this point first unlock all the necessary drills (those which are used most often- press the play, video analysis, hold the line, defending crosses, skill drill, pass go shoot, shooting, one on one finishing, warm up, stretch, gym, long run any other that you consider is good for training your players) and then upgrade them to next levels.

Feel free to ask anything. : )