I find that coaches are hard to find with 7 stars but you can hit 5 and six easy.
Fitness coaches and goalkeeper coaches = self explained
Shooting coach needs Technique and attacking
Ball Control is Tech and Def
Attack coaching is obvious
Set Pieces are weird its kind of attack tactics and technique
This may be gospel or i may be slightly wrong please feel free to put me right but these are the coaching stats i look for and i do alright with tugs training.
Motivating and Determination are good attributes too.
Hope this helps a bit for ya