Regarding the thing about Vader always being Luke’s father, I found some info about why Lucas might have said this.

Originally, in the very early drafts, there were two characters. Kane Starkiller/Akira Valor/The Starkiller, a half-machine/half-man and Jedi-in-hiding, who is the father of the main character Annikin Starkiller (who’d later go on to be Luke Skywalker). And Darth Vader, a general for the Empire. The two characters later became combined into one.

George Lucas said:

“Well, to be very honest with you, when I wrote the very very first script it was about Annikin Starkiller and his two kids. And, uh, he was a rogue Jedi, and there were remnants of that [draft] that found its way into the final Star Wars.”
-MovieFone Unscripted, 2005

So from a certain point of view, Vader was always gonna be Luke’s father. It was just discarded but then we ended up getting something that more resembled the original idea.