From my time here, I learned that the less you read Zach's posts, the better it is for your mental health.
Gundogan will be tough but not impossible to sign. He isn't a top-20 or such player in the world. Those we can't sign. But need to move and wrap Gundogan early (which is exactly what Marotta and Paratici are trying to do), like by March like we did with Dybala. With Gundogan it's even more imperative of course. Come season's end when other top club's start their mercato wheeling and dealing, it'll be tougher.
We usually get the best out of players, so Fabregas would be a great signing.
Oscar would be a meh signing. Moutinho would be another meh one.
Isco of course would be an amazing signing.
If Pogba leaves (decent chance of that happening of course), then I wouldn't be surprised if we sign two of the attacking CM types. One as mezzala aka Pogba's replacement, the other for the AM role. Allegri likes this almost CM type AMs who can defend. Plus, the player would be able to start in a 352 when we play that tactic whereas a genuine AM would sit on the bench.