I'm not anyone involved with the people who make it or anything, but I have bought the game and I think I can explain the questions you ask
Number 1... You ask why doesen't hiring a trainer increase the percentages on the training screen.
Well actually it does when you train up certain attributes, so say the guy you hire is a specialist in teaching volleys when when you train volleys on your player or players then they will go up faster than if you didnt have a trainer.
Number 2...There is actually an energy bar, its the ones called Short term Form and Long term Form, they both actually mean the fitness/energy of your player.
I do see what you mean when you say about energy though, because in a match energy and form are 2 different bars and I dont see an energy bar in the training screen. But I think maybe the short term form of your player influences the energy a bit. And also if you train him hard before a match his energy might drop slightly.