But do we really know for sure that Lucas didn't originally intend Anakin to be Darth Vader? I mean, I've long theorized that he invented that bit some time after he made the first film, but I don't know.

And what about after Empire Strikes Back came out and from then on down to when the prequels started to come out in 99, was there any sign whatsoever of the celibacy thing, even a hint?

The celibacy thing does fit with the sort of person who would give up all possessions. I know the EU authors certainly didn't seem to have celibacy in mind, they got Luke married.