United should be all over Sancho. He is young, English, extremely skillful and fills a gap that has existed for far too long. A front three of him, Rashford and Martial could be deadly!
Defenders are a tricky issue as left-back and a defensive mid are the only positions where I can see United buying the type of player they normally target and obtain an improvement. Elsewhere, you need to buy a world class player in order for them to get into the side (think Koulibaly) and are they really worth it in the current scenario? I believe that even for the positions mentioned prospects like Williams and McTominay should be a reasonable fill-in to see how they develop instead of buying a player who is only slightly better. Another reason why I really believe United could go all in for David Alaba; he is a world-class player who can play as a left-back or as a centre-back with Maguire compensating for the Austrian's aerial weakness. You could also have him in the centre of midfield should the need arise too.