No. Teach science and teach about religion and religions. Teach about everything ideally. No limits.
Yes. After all, you go to school to learn. Don't censor the material for the students. Surprisingly enough, they do understand and comprehend more than what people give them credit for.
Ideally, yes, but I would worry about a secular institution delving too deeply into religion, and also there really are separation of church and state issues, IMO. One that I know of right now is what's to stop a Muslim from getting in and preaching the Koran. I don't think that sort of thing should be going on - talking about how a creator may have created the Earth and the universe is to me completely unobjectionable and could be easily objective, especially considering how evolution through natural selection is anything but provable. Purely theory.
This is the only problem I have with that argument. Schools (even as far back as when I was in it) taught world religions. No one says that the teach has to hold Sunday school lessons in class, but at least cover Christianity and Intelligent Design in the same light as the other major religions in the world. (And teach it in History class, not science.)