We just finished CLUE a couple of weeks ago and had a blast. We built several door units and used the main floor area for each room. We had a long dining table - made with tall desk units we already had from our production of Radium Girls - that rolled out and back. It was a super easy scene change for that particular scene. I have seen pictures of sets ranging from two moving doors to very large sets with a second floor. All of them work!
We purchased the use of the tracks for the music and I'm so glad we did. One of our stage managers worked the sound effects and music so we rehearsed with it for a few weeks which was very helpful. The piano accompaniment would work well, too. The show needs the music either live or recorded - it adds so much!
Someone else mentioned walked around the theatre and commenting on Boddy Manor. We did that as well and the audience (and cast) enjoyed it a bunch.It's a fun show - have a great time with it!