Eric Steele is a far better goalkeeping coach and was very involved with the early development with De Gea. Woods is OK but like the rest of the coaching staff most of them inexperienced in coaching. Even though some were good players that does not make them good coaches and there lies a lot of Moyes problems'
As far as SAF coming back he would have to start from scratch with a coaching team as most of them have moved on and would only come back in an elevated role or were promised so much when SAF gave it in again.
Its not just a question of getting coaches in, you have to try them out, develop them and still manage the greatest club in the world, Unless you have a very experienced manager who has done well in most areas in the game it will all be the same. Moyes had very limited success but not in the big time and to get where the club would want him to be would take a few years and that is something Manchester United will not give.