That's what I was thinking, too. The trickiest part is incorporating the stretching gallery, since it has to be directly beneath the cupola and still have room below it to stretch. I was considering placing the seance room on the first floor directly below the stretching gallery, so that the stretching would push the seance room underground and allow access to secret underground passageways. But in the ride, the seance room is on the second or third floor, adjacent to the ballroom. So now I must decide which option I want to take, or come up with an entirely new solution.
The trick is to keep the original feel of the mansion, preserve the interior and exterior appearances as much as possible, and NOT OVERDO IT. I could pull a Hogwarts and make the mansion an impossibly huge residence with innumerable rooms and passageways, but that's not exactly what the ride is about.
I'm also trying to decide if I'm going to use the entrance hall from the movie. It's a lovely set, and it's derived from early sketches for the ride, but it's not actually in the ride...so I have to decide if I want to use the DL foyer, the movie entrance hall, both, or a combination of the two.