Fang Zei said:

Zombie probably answered this question in his book, but I'm too lazy to look it up so I'll ask it here:

Was the original plan (circa 1980) to just keep going and make 6, 7, 8, 9, etc, or was George already planning on doing the PT before the ST?

I remember seeing a tv news story on youtube from, I think, the time of Empire's production/release where they're interviewing Hamill on set and he says "I can't wait to see the earlier trilogy, the one I'm not in."

Zombie recently posted a masterful & authoritative article on secrethistoryofstarwars.com answering every question on this issue that can possibly be answered.