I think this is one of the most awesome things I've seen on Eurobricks--I've been lurking on this site for over a year now, but this post was enough to get me to finally register so I could comment and join the discussion of this great project.
I've been working (very slowly) on a cloud city project of my own, although on a much smaller scale (maybe 1/3 the size). I'll certainly incorprate some elements from this into my own cloud city.
A few comments and/or suggestions:
-I really love the middle floor, especially the catwalk and the way the back wall really captures the feeling from the movie. Really an epic job.
-I own the death star, but I'm having a hard time comparing the size of your cloud city to the death star (other than the piece counts you mentioned). Is this set similar in diameter to the Death Star?
-The big white open area on the top floor, as well as the dinner (where Vader waits) room on the top floor appear bigger than they need to be. Could you use that space more efficiently to add other play areas (maybe some corridors, or just additional rooms (not necessarily from the movie)
-I really like the window overlooking the bridge/landing platform. Can you add some sort of window pane there (i.e., so there is not just a huge opening)?
-Could you add a conveyor belt or something to junk room/furnace room? For some reason, I picture the junk room (where Chewie rescues C-3po) on the top floor with the living areas. I wonder if you used the space on the top floor more efficiently if you could squeeze it in up there (I see you already have a cool little bonus room on the top floor).
-I like how all the rooms on the middle floor flow together. However, is there enough room behind the carbon freezing platform to fit a hand through?
-I'm having a hard time seeing from the pictures whether the archway at the base of the catwalk (opposite end from the "I am your father" moment) goes anywhere. Where does that arch lead to? Can you post a pic showing that area in more detail?
-I would guess that anyone who is going to pay $400 for a set already has several Chewie, R2, and C-3po already (although I agree they are important for most cloud city scenes). I would prefer to trade those out (as well as white shirt Han) for a few generic cloud city citizens.
Thanks again for sharing your fantastic project. This inspires me to get going again on my own cloud city project, although, I'm half tempted to abandon that and try to build something larger along the same lines as what you've got here.