Over 10 assistant coaches & goalkeeper coaches combined will cause loss of training for the week.
Some goalkeeper trainers prefer to keep relatively fewer goalkeeper coaches (as few as five) and relatively more assistant coaches, arguing that the loss in training speed is minimal and the gain in form is worth it. The effects of this choice have not been studied.
Research suggests that starting from a 17-year old solid keeper, training with five goalkeeping coaches requires only one additional week to reach divine skill compared with training with ten goalkeeping coaches. This information has been posted in the Newbie Conference. (A more precise citation would be appreciated.)