Dunst is a terrible MJ. I don't buy her as a model, an actress, or someone Peter would lust after for whatever reason.
I certainly wouldn't lust after her for any reason.
She looked good in Bring It On.
Pretty much what they'd have to do. Although in the comic-book world I think Oscorp creating an uber-powerful living symbiote seems to make less sense compared to an alien costume acquired in another dimension. Uber-powerful sentient robots, that's another story.
Movie-wise, keeping Oscorp in the middle of things would make more sense than the comic version, or even the cartoon version.