And as for Star Wars being episode 4, Lucas also said that he had this rough outline to a story, took the most interesting part, ie the middle, and fleshed that out into a film.
I'm not saying he had the whole of SW already written out, but that he had an idea of what he wanted to do.
Watch some OLD docus about it. This was Lucas before all the bullshit, when he knew what he was talking about, unlike you.