As far as the 20 year gap goes, I'm thinking in those terms because I'm thinking I'll use the idea of the Emperor not being defeated until episode IX. However, I'm toying with the idea of Vader still being defeated in episode VI. This has been inspired by considerations of the 'universe-shrinking' many members have been complaining about. I think the cause of this is less the discovery of relationships between the characters and more the fact that the focus of the saga has been narrowed to the story of one person, Anakin Skywalker. SW '77 does not have this narrow view. It is a snapshot from the story of the rebellion against the Empire and the story is not restricted to any one of the people we meet. It is the story of all the characters.
I think this is another reason why Luca$h's PT is less satisfying, that it has been reduced to the story of Anakin Skywalker, that he is "The One" and that everyone else is a supporting character in his story.
This is why the use of the droids appeals to me so much. They are ageless and are the perfect characters to take us through 60 years of history. They provide a constancy against which the transience of the organic lives around them can be highlighted. Their memories are manipulated, which prevents them from becoming too god-like in their knowledge of the overall story. They are thrust into situations in the same way as the audience, which means that we find out things and meet characters as they do.
The time scale I've mentioned is not set in stone, by the way. It's merely a tool to work towards a structure for the saga.