It's very tempting to get ahead of yourself when designing these sort of things. My advice would be to keep the forshadowing and mystery to a minimum for the first episode. At the same time you want to set up the premise of the show quickly. If it's a hospital show then your character should probably have a job there by the end of the first episode. Same for a cop, university student etc.
As for the voice over, that is entirely up to you. Thinking on it for a moment though, will you use the voice over after the first episode? Will you continue to use it throughout the series? If the answer to either is no, either don't use it or find some reason for it not to appear after the pilot. (Eg the character was telling the day back to someone else)
Hope that helps a little.