I'd sell Fellaini, Evans, Valencia or Young, Hernandez, bring back Nani and obviously not bring back Falcao, and try to minimize the amount of change made, buying a couple superstars (even if the prices were astronomical) rather than a bunch of new players. The following guys stay:
-----Rooney----- (RVP, Wilson)
DiMaria-Mata-WF (Januzaj, Nani, Herrera, Rooney)
------Herrera---- (CM)
-----Blind-------- (Carrick)
Shaw--------Rafael (FB, Valencia/Young)
---CB--Smalling-- (Rojo, Jones)
------De Gea----- (Valdes, Young Goalie)
Then it's just about value and who we can get, depending on if they'll come, will their club sell and are we in the CL.
WF -Reus and if not him then Bale, and if neither Depay. We need goals from out wide. Sanchez would have been perfect, sadly.
CM - Koke, and if we get him he starts and Herrera/Mata fight for a place. Verrati would be worth a massive bid, too.
CB - Laporte is already solid and at his age will only improve.
FB - A player who can cover both sides and doesn't get hurt. Tempted to say Darmian after this summer but I don't really ever watch Torino. Clyne is good enough too if we think he'll stay healthy.
Then see how we do and in the summer of 2016, replace Carrick with a CM who can compete with Blind and RVP with a new 2nd or 3rd striker depending on how Wilson's development goes. If Smalling or Jones haven't stepped up, sell one and replace with a new CB.
I'll add that despite the last paragraph, though I haven't seen Malaga much this year, Ignacio Camacho is now in the Spain squad as a midfielder, aged 24 and not at a CL club and so should be signed immediately since it really can't go too wrong.
More likely, we'll have to shop a bit less ambitiously, so I'd be very happy with a summer of young talent like Depay, Kovacic, Laporte, Darmian/Clyne and if we take 2-3 years to build, that's fine. Everyone but Di Maria and Rooney that I think will be good enough to start for a treble-fighting side on the team (De Gea, Herrera, Shaw, Rafael, Januzaj) are under 24 anyways.