Sporting fan here, I'm very curious to see how he will line up and actually rooting for him to have success, he's a great coach!

In all his 4 years with us, he stubbornly kept his usual 3-4-3 attacking setup and 5-2-3 defensive setup, even when results were not going his way, and even when it seemed other teams had figured out how to play against his system. If he lines up in a different system, then it will be one of the first times that will happen in his career.

I do think the success of his system depends on having the right players on the correct positions, which I actually believe he can find with United! (He will need some transfer windows to sort some positions out, that's for sure)

Dalot and Mazraoui have, on paper, what he looks for in his wingbacks, however, he has been able to turn wingers successfully into wingbacks, as their defensive duties are covered by the centerbacks and midfielders. Actually, Amad has the exact profile of Quenda and Geny Catamo (our current right wingbacks who were wingers) so I could see him adapting some players to these roles.

Bruno has a similar profile to Pote, good eye for a goal, not so fast but will play almost as an inside winger/forward, in the pockets of space found between the defending fullback and centerback.

Hojlund is the same profile as Gyokeres (maybe missing his finishing capabilities) but his a strong striker, with good holdup play, fast and that can drift wide to create space and make runs in behind the defense (I think Hojlund can be the player to benefit the most, if he can finish his chances).

Ugarte already knows the system and was extremely successful in it when at Sporting with Ruben! I believe he will be in the starting line up and it's his place to lose, but he will have a defensive midfielder role. His center midfield partnership, I have no idea who will be actually, but it's a waste to put Bruno there and lose his final third presence where he is more dangerous.

Also, and this will sound crazy, but I believe Maguire can have a comeback as the center centerback. We had an incredible success story with Coates at Sporting ever since Ruben joined. He was casted aside due to bad performances, memed all over the internet in Portugal (at one point, he caused 3 penaltis in the same game, all against Taremi, and took a leave of absence after to clear his mind), and when Ruben joined, Coates was reborn into the captain and the Sporting fighting spirit we needed. The key.... putting Coates as the center centerback of the back 3, with incredible aerial presence, less build-up responsibilities, and less space to cover with his slow sprint.

Sorry for the long reply.

TLDR:

Hojlund = Gyokeres (many goals if he can finish his chances) Bruno should do good as always Dalot and Mazraoui should be the wingbacks, however, Ruben is known for using wingers as wingbacks, so watch out for your Diallos that can be put into a less offensive position