Some thoughts on United. I can see Mourinho employing one of the 3 main systems, 4-2-3-1, 4-3-3 or 4-4-2 "diamond." Let's talk about each one in order.
4-2-3-1 would be the most balanced and most conductive to Mourinho's patented counter-attacking game, but it just doesn't fit United summer transfers and key players, unless Mourinho wants to walk into a bitter conflict right from the start. The first problem is that there is no satisfactory way Ibra, Rooney and Mkhitaryan can be on the pitch at the same time; none of them are any good on the wing and there are only 2 available spots in the middle. Also if that's the basic system, I don't know why United would want to buy Pogba, since in Mourinho's 4-2-3-1 both CMs sit in front of the defense and rarely join the attack – that's not what Pogba is about at all.
4-3-3 would perfectly suit Pogba and Ibra, but not many others. Once again Rooney would have to be either on the wing or on the bench, same for Mkhitaryan (he did play as a CM in Shakhtar, but I highly doubt that he is disciplined enough for that role in Mourinho's team. If he plays, it would be at #10 and nowhere else). And with Martial surely too young to win Mourinho's trust at this point, United have no great goal-scoring wingers who can support and play off Ibra the way Chelsea's wingers supported Drogba and Diego Costa. This system would also rely way too much on 35-year-old Ibra as the only striker capable of being a focal point in attack.
Finally there is 4-4-2 "diamond", not one of Mourinho's favorites but one he did use in the past, notably when trying to integrate Shevchenko into Chelsea's game (which failed). This system would allow for all 3 of Ibra, Rooney and Mkhitaryan to be on the pitch at the same time, while making good use on United's CMs (including the possible signings of Pogba or Matuidi) and attacking full-backs. This would mean the likes of Depay and Ashley Young would be frozen out of the first team (which wouldn't be such a great loss for them) and the only possible downside would be the relative lack of pace through the middle when Rooney and Ibra are playing alongside each other (which can be corrected by bringing on Martial or Rashford). I think this is the most likely route, given United's transfer strategy this summer, however this is Mourinho's least favored basic system and the only one that didn't win him the league in the past.
To conclude, I don't see United under Mourinho as an instant success. He will have to choose between alienating key players or using a system he himself doesn't trust; unlike 2004 Chelsea or 2008 Inter, the team has no obvious core of experienced players that fit into his style – their best talents are younger and it's well-known that Mou doesn't trust youth. There will be a lot of change and upheaval in the seasons ahead and the only way Mourinho can build a title-winning side out of this team will be by completely rebuilding it over the years and weathering all the storms that will come with it. I wouldn't necessarily bet against that, given the resources at his disposal, but he would need to show a new level of calmness and maturity to succeed at United.
Good post.
I think Mourinho's done the weird thing of buying for a year in an attempt to just get them back in the top 4. There's no way he envisages this side carrying them forward for the next 4 or 5 years. Whilst he's bought good players, he hasn't bought any of Europe's young or prime-aged (sounds like a steak) superstars. He's paid top bill for Zlatan and Mkhitaryan because few others were prepared to pay those weekly sums for players.
There's no pace in the side, so I'm not sure how he's getting a 4-3-3 to work, and there's little width apart from what Shaw and maybe Darmian can offer from full-back.
I think they'll make top 4 - which is his sole aim - but it's won't be pretty. He'll then build an entirely new, younger side from next year onwards knowing they can attract better players, and he's had a year to work out the side.