On the whole Iger and Feige issue, I think a film on the level of the first two X Men films , would be fine in terms of the balance between story, issues, and spectacle.
While they didn't involve Infinity War level threats , they were consequential events, as opposed to Spiderman Homecoming, which really only effected Peter's life and his immediate social, and family life, or a film like the first Antman .
In terms of the team , I think the it should be made up of mostly familiar X Men members , as opposed to a bunch of lesser known characters that only comic fans know of .
I think you've got to at least have Cyclops, Jean, and Storm, while I think Feige will have Beast is apart of the team regardless, even if he's not a must , for this film .
Aside from those 4 , I think they can switch it up with members who weren't fully exploited in the Fox era , or characters who haven't been adapted yet.
Magento doesn't have to be the villain of the first film, and if anything, I'd prefer Mr. Sinister as the baddie .