1) Dramatic choice, probably.
2) I'm pretty sure Hickman doesn't give a damn about "The Man Called X". It's also likely Xavier didn't know the role of the likes of Hope, Goldballs and Tempus at the time, and in anyway I don't see why he wouldn't trust Scott with them.
3) They seem pretty clearly the same. I don't see them as being more malleable- Scott specifically is seeing Xavier do what he wanted to do with Utopia on steroids.
4) Plans the next step, of course.
Magneto was crazy and dangerous. He only met Charles and Moira around the time of UXM #150.
I don't see it. Xavier and Mags delivered a nation with the chance of eternal life.
I got nothing here.