Did you Lucas have more ideas outside the original movie, I believe he did. Was anything written in stone, that is where I believe that not to be true. I'm sure when he was writing out the original Star Wars, I actually do believe he had other notes on what happened to everyone and how they got there. But I believe they were just rough draft notes of basic ideas.
Lucas probably had a million ideas of maybe Vader was Lukes father, or maybe he killed Lukes father? Who is the emperor, and will we ever see him if I make a sequel, nah, maybe just let people imagine this great ruler of the galaxy. In the end he probably had a million different ideas jotted down in his binder, some he used and some he threw away.
The one big lie George says presently is that the saga was always about these two twins and their father (This was said on the documentary on the OT DVD release) That is a bunch of B.S. I don't believe he ever had intended when he made the original SW for Luke & Leia to be siblings, hence the whole family affair idea doesn't work for me. I think he went with Leia being Lukes sister, after Vader being Lukes father went over so well with the public, that this would be the 'twist' for Jedi, but it had the opposite effect.
As for 12 episodes or 9 episodes or 6 episodes, I believe at one time when Lucas was still hungry and creative he may had a grand design of say 3 trilogies of SW films of 3 generation of Skywalkers, but then realized he didn't want to spend the rest of his life with this project anymore. That is why when Lucas says it was always 6 movies, the birth, life, fall, and redemption of Darth Vader, that is a bold face lie too.
Did Star Wars need any sequels, not really, but the OT works for me well. The original is still my favorite movie of all-time, but ESB is #2 right behind it, and though I feel it is a better movie than the original, the magic and charm of the first one always wins me over in the end. Jedi, though it is a good movie, is where Lucas began to lose his creativity, and if hindsight was 20/20, after analyzing what is wrong with Jedi, I would have never gotten hyped about the prequels, cause I feel SW hit the pinnacle in 1980, and I don't think Lucas had the hunger to make another classic movie, he just wanted something good enough, and in the end, whether we like it or not, he has made a boatload of money off of a whole trilogy of inferior films compared to the OT. But as I said, I still like Jedi alot because it does give closure to the saga, which is like closure to our childhood, and the end with Vader/Luke/Emperor is as good as Star Wars can get.
Overall, I really don't listen to Lucas much anymore about his grand vision, because you can google some old interview from 15-20 years that will contradict something he said. It is a shame because he wants the saga to be about Anakin Skywalker and it just doesn't sell to me, I grew up with the story of Luke, and that is how I will always see it. It is a shame because the younger generation who love the PT now are missing out on a great experience of just watching the original Star Wars for what it originally was, a fun space adventure with lovable characters and really cool bad guy. Now they look it at as some inferior special effects movie, that is totally out of place with the first three prequels they just watched. I guess it's their loss.