Did George Lucas have a plan for Star Wars?

Sure, here's a question based on the given paragraph, simulating the tone of a questioner: "It's often said that George Lucas' vision for Star Wars was grand and sweeping, but did he really have a concrete plan for the entire saga from the very beginning? Or did he stumble upon the idea of Episode IV: A New Hope and then gradually develop the rest of the story as he went along? Did he have a clear roadmap in mind, or was it more of a case of making it up as he went? It's fascinating to think about the creative process behind such an iconic franchise, and whether Lucas' original plan was strictly adhered to, or if he had to make changes and adaptations along the way.