Yeah, like you say, it's a crazy amount of money for someone who wouldn't easily slot into the team. Like he walks in, but there's a lot of adjusting to be done to get our 2 100m players to perform basically, and the only way to do that would basically be to do away with wingers entirely and have 3 attackers who rotate around as said before. Also as you say, with a proper holding mid like Carrick, pogba does look a lot better.
No doubt in my mind that we'll go for him though, get the feeling that Mourinho wants something like this for next season as his main 11 for the majority of games:
De Gea
Valencia Bailly Gimenez Shaw
Holding-mid Pogba
Mata Griezmann Mkhitaryan
Ibra
Obviously with Ibra's age, maybe he hopes Martial adapts to his style more and then he can slot in up top for Ibra. Same with Shaw getting back to his best under Mourinho. Someone like Herrera would be the first option off the bench or someone who comes in all the time whenever it's a tougher game, or away game to make it a more solid midfield, alongside pogba and the new holding mid, while one of mata/miki/martial or ibra/griezmann (probably not since he's gonna be the big buy) drop out. So in that case, I really can see it working, but at the same time, the one obvious thing that our entire season next year can hinge on is getting that holding position right. Replace Carrick properly, and we can get the best out of Pogba and someone like Griezmann at the same time (and allow us to play both Miki and Mata as well). Get it wrong and we'll be disjointed as always.