Another one I'm very jealous of, to have not just one but multiple meticulousl organized and curated otaku rooms for different purposes.

But that said, my absolute dream otaku room is to have a 1:1 re-creation of the SOS brigade clubroom. Unsure whether I'd want the furnishings to remain exactly the same with a few figures here and there (the table in the center would be the dedicated display surface if this were the case), or if I'd want to cover the walls, bookshelves shelves, etc. in Haruhi and other golden age and prior otaku memorobilia.
Also don't know what I'd do about the window; if above ground then of course it'd be real with the actual view outside of it, but actually ideally it'd be underground with a facade that emulates the view of the courtyard and main school building. If it makes it easier, how it looked when in Closed Space works too.