Strange has tended to work best when an artist (Ditko, Colan, Brunner all come to mind) sticks him in the middle of some crazy shit and draws the living hell out of it. Even good writers have trouble making him compelling outside of that, though.
He does have a decent origin arc: selfish rich surgeon suffers an accident that leaves his hands useless for surgery, but his self-pitying ass is rescued and revived when an ancient master recruits him into a world of magic. When his master is killed, he faces off against mystical foes with incomplete training, and becomes a Sorcerer Supreme by finding his inner whatever.
(I didn't say it was an origin you've never seen before, but it was a bit fresher way back when. Variations have been worked over the years).
He has to be mature enough to be convincing as a guy who's been a big-time surgeon for a while, but obviously young enough for a studio to ink him to a franchise.
Ben Whishaw might not be a bad choice-- he's a bit young now, but I suspect he'll have matured a bit when they get around to it: he can certainly do arrogant.
