Worth noting, as that ANH novel stuff is mentioned (though GL didn't write that himself), that GL had the backstory with things like the Commerce Guild and Banking Clan and all that all the way back when he first came up with the story in the early/mid 70s. Like the name Mace Windu, it took him more than a quarter of a century to get those ideas on screen!
how much of the PT's did he have planned out? they show his notes on the yellow pads in the PM DVD extras, I froze them to see and it had stuff about Anakin being a slave. He says he never had the play by play written out, but he certainly had the major events and a timeline for them in his head. I would love to just sit and pick his brain for a few hours, he knows tons of history, religions, philosopy and all the creativity he has is just astounding.