Ah Iceburn, you're gonna need the masters bedroom for your collection size and especially since you keep the boxes..:D I used the second largest bedroom in my house. At first I thought it would all fit in, but then I still have other figures waiting to migrate here and also I have other toys I want to display and already little room. I already moved my Comics collection to my bedroom as there's no more space for these shelves. I might even move my PC to my bedroom later on to get more shelf space.
As for keeping MISP/MISB - naaah I just keep the boxes I think look good, but I certainly keep them out of the their casings.. With the exception now of movie legends and a few Spychangers.. they dont take that much room anyhow ... I haven't decided if they will be let out just yet. Before I used to keep the backing cards ( Cybertron series) , but I threw them away when I moved to my house. Shoulda kept them actually as someone here might have better use for them. :)