Agree that he needs proper resources, both on and off the pitch, but you can bet the doom mongers on here will be shouting for his head before Christmas if we have a poor start, regardless of who comes in.
SAF came into a similarish situation, and gradually changed lots of things, academy, scouting, coaching, as well as player personnel, and it took him over three years. ETH will not get three years of poorish displays before he gets the push, although I think our football will be a lot better in regards to looking like a team instead of 11 individuals.
To me there are two, or three, scenarios that could unfold, in one we buy in four or five new players, in which case the club would-be looking for instant success, like José, or two, we give our very good, but still unproven, academy players the nod, and try to develop the team over a couple of seasons, or three, just two or three new additions, two or three academy players in the match day squad, and (hopefully) a new lease of life for some of our poorer performing players from last season, and there were quite a few.
Realistically, it will take ETH at least this season to weedle out the players who will not, or can not, adapt to his way of playing, but I firmly believe that every player still on United's books on the first day of pre season, will be given the opportunity to show the manager what they can do, and hope some get their mojo back.