I love your ambition, Ilanthar! I know what you mean, though; it took me several attempts at a single palace to figure out a few tricks that made things easier, and even after my month-long mapping in April, I'm still doing things that have to have easier methods that I just haven't figured out yet. I restarted my city map so many times and I still don't feel like it's right. I really admire you for doing this and doing it so well. I wouldn't have known you weren't completely familiar with SketchUp just from looking at this.

For the narrow corridor there, you could just turn it into a wall and wouldn't have to move anything. It could just be a way to divide "wards", or maybe an emergency system in case of fire; the doors in that wall could be fire doors to help keep the flames contained to the originating ward. I imagine an arc like this would need something like that or fire could potentially run rampant.