Great ideas around here.

When I did my 4h40 long silent edit (2 parts) I wanted to stay as close as I could from the original story and I did not care much about the lenght of the scenes I cuted because I knew the music will blend them well together.

IMO the most difficult thing in a 3 hours "normal movie" will be to keep the scenes long enough so they will not seam too rushed. The main characters needs time to speak so a lot of second characters will have to shut their mouth! I think it has to be an Anakin/Vader movie, so you'll have to make heartbreaking things like turning Han Solo into a quite minor character (screentime-wise).

And another thing that should be kept in mind: the age of the actors... Ford did look older in Jedi than in ANH, and so the others. You can't put Solo helping Luke to destroy the Death Star at the end of the movie if you already used ROTJ footage of him earlier in the movie for exemple.

But I'm sure you already thought about all of this. Just few thoughts as I was reading this thread.