Re: Lost (no spoilers please)
We're still not quite sure where Ethan came from. I never considered that he may have been on the crew, but as you said, I doubt it. I'm sure it'll all be revealed at some point.
As for the psychic, I'm sure he knew the plane was going to crash and that was the only way Claire would end up keeping her baby. Remember, he specifically told her that she had to get on that particular flight.