Do i look at the casting director as if i'm speaking to him/her?
It really depends on the audience and the piece itself. If it's a serious monologue it's best to kind of look through/over the audience, but more humorous ones tend to look at the audience more, still not directly. But if you want to make the audience uncomfortable if it's an uncomfortable piece by all means stare away. Good luck! :)
No. Never do this. I go to a performing arts school, and we've been told not to look directly at the audition panel when auditioning as it can freak them out