I've heard people say they've wanted Jonny Depp for Doctor Strange. I'm not totally against it, but I always thought there would be someone better.
However, if they are building for a Defenders movie like they did for Avengers... they're going to need at least one Robert Downey Jr level actor to draw a crowd. And I think Jonny Depp could be that guy.
As far as director? Part of me would love to see Terry Gilliam take that on. I'd love a bit of a psychedelic take on it. However, I've heard he's a little slow and difficult to work with. So my second (and possibly better) choice would be Guillermo del Toro.
And lastly, for a Defenders line up? Ant Man and Doctor Strange seem to be a given. But, I don't think they'd steal Hulk away from Avengers for film.
As Greggie said, I think Fox has the rights to Silver Surfer (did you mean to say not sure?)... but I don't know if they have the rights to Namor specifically. I could be wrong. Not my favorite character though.
I think Black Cat is a given, and Iron Fist would round the team off nicely.