Deciding on my film...

So after doing our pitches yesterday, I have decided to go forward and the my script about the geeky boy, convinced by head cheerleader to kill her boyfriend. I really want to make their characters sort of a quirky spin off to film noir. I want to keep it modern day, but give it the voice over techniques coming from the voice of the main character Morty, and give Natalie the femme fatal look. I still haven't really established the way in which I would want Natalie's boyfriend to look like as of right now, because I'm still working on the two main characters. When thinking of who I would cast for the role of Morty, I was thinking about actors such as Colin Hanks, Topher Grace, Lucas Grabeel, Mitchel Musso, Steven Christopher Parker, or Michael Cera. For the role of Natalie, I would cast someone such as Kirby Bliss Blanton, Selena Gomez, Ashley Tisdale, Sophia Bush, Erika Christensen, or Leighton Meester. I want Natalie to be very sexy, but yet harmless looking in the film. When it comes to her boyfriend though, I think I want him to be an ideal jock, but also with a soft side, not scary looking per say. Someone like Channing Tatum.... but that's all I can think of at the moment. I definitely will have to get deeper into his character and characteristics before trying to think of someone to cast his part. But other than that, that is as far as I have gotten to far with my movie... still brainstorming!!