well in my oppinion u shuld have at least a lvl6 coach. depending on your finances, but a lvl 10 is the ideal.
about the players that train, well, when u choose the type of training u can set the positions that will benefit from training. players that train at least 48minutes per week will benefit more from training, the ideal is to have the trainable players to get 48 minutes of playing or somewhere near that time, because if they play for example 80minutes, they will have less % of training, but i can´t tell u how much. read the help file because they explain it betther. cheers