C.P.
These are all amazing ideas, but I STRONGLY suggest that you give them the tools to do these things, all boxed up, and do it together, or even let them do a mural themselves on one wall.
I've noticed a trend. The clubhouse gets a lot more time and attention from the kids if they do the work themselves. It's also a great time to use the experience to teach life lessons about safety, friendship, preparation, foresight (are you going to like this in two years?), etc.
Good luck! And this is a GREAT idea that I am thinking of using for my boys!!!
Uh...the closet clubhouse, not the sparkly chandelier! ;o)