It's close to 2 1/2 feet wide by 1 1/2 feet long. So, yeah, it's on the large side. Each level loses a bit of that "fin" look on the front, so that the third (top) level is a circle with a 1-foot diameter. Then, off the back of the structure, I'll add the gantry, which will be another two feet long or so.
The second level will hold the torture room, the cell, and the junk room/boiler room. Then the top, circular piece will be the Carbon Freezing Chamber. Off the back, Luke and Vader wil be able to duel through the control room with the big window, out onto the gantry.
I always thought of the CFC as the bowels of the city, too, but I put it on top since it's the most important thing in the playset, and as a level by itself was going to take up the least space.