He would be a bit more of an unconventional choice, but I've thought for awhile that John Krasinski would be an interesting choice for Reed. He was almost cast as Cap before Evans was, plus he was considered for Starlord as well. If they are aiming for bigger name, then I like the Levitt or Gosling suggestion. But I would agree that Levitt strikes me as the better bet as far as being willing to stick around longer between those two.
I like the Lilly James suggestion for Sue.
I would also want them to cast someone close to Holland's age for Johnny. I wouldn't mind seeing Charlie Rowe considered. I think he's a promising actor, and he was the runner up for Spider-Man.
Seth Rogen has also been my unorthodox choice for the Thing. Plus, he has good chemistry with Joseph Gordon Levitt, so I think they could sell Reed and Ben being old friends if they were both actually cast. If not him, then I think Joel Edgerton would probably be my safe choice.