I think in the long run having three guys who can all play up front and switch roles at will like Martial, Rashford and Mbappe would be quite an ideal threesome up front. We'd be just great on counters because they're really pacy(+Pogba making the passes and also very quick, Herrera and Miki also...). And I think they'd be good in a positional attack as well because they can beat their man.
That was my idea with Martial, Rashford and Depay - having three pacy, technical guys upfront, all with a good sense of goalscoring and all three who can interchange positions during the game.
Mourinho never tried this because his idea was/is to always play Zlatan, so Martial and Rashford were pushed out on the wing, while Memphis was pushed out of the team. I am not sure Mbappe has more talent or more skills than Memphis. He is the player of the moment, having showed great talent and also excellent numbers, but he would cost a king's ransom without guaranteeing to improve our team. Would I like us to buy him? Yes, I definitely would as he is one of the most exciting young players in Europe, but I still think we should leave the striker's position for Martial and Rashford and buy a proper winger instead. Bale is still number one for me, but this Summer would be the last chance for him to join us, as he will be 28 in July. If not Bale, we might also try to bring Alexis Sanchez. I was so keen for United to get him when he was leaving Barcelona, but we might have the second chance at the end of this season. Neymar is younger than Bale and Sanchez, but nothing can guarantee that he would light up the EPL like he is doing in Spain. He probably would, but I am not sure he is worth five or ten times more than every other winger out there. I also can't stand his constant simulating. I think we might have tried to buy Ousmane Dembele last Summer, but this train is gone for now. Another Dembele we might try to buy is Moussa Dembele from Celtic. He might be as good as Mbappe, but costs two or three times less.
Now we need someone great to be the deep playmaker. A young Carrick/Xavi/Pirlo type of a player, then I'm not sure whether there is much more we need in the first 11..
Maybe we should just buy someone like Bakayoko from Monaco and let Pogba do the playmaker, with Miki/Mata in front of them as number 10? Otherwise, it would be Pogba and Herrera in front of a defensive midfielder, with Miki on a wide position.
I would also not give up from signing Alcantara, if any possibility arises. I am afraid he might go to City if they play in the CL next season and if Guardiola stays. Sooner or later he will want to try his luck in the Premier League and we should be the first team to get him if he decides to move to England.
Talking about Monaco, they are one of the rare teams I would rob for more than two or three players. Fabinho would be a great buy as well, while I also like Bernardo Silva and Lemar, two very technical and tactically intelligent players. However, if I could choose "only" two, I would choose Bakayoko and Fabinho.