We live near DC now too. I would definitely recommend staying in a suburb and taking the Metro in (I can give you some towns that we usually use). We've lived close for over a year now and I've never driven in close to DC, it's just bedlam. Manassas is crazy enough for me and it's not nearly as bad as Fairfax or Arlington.

Allow me to recommend the Holocaust Museum. It's a less popular museum but it's fascinating (at least I think it is). I am also dying to go to the Spy Museum.

Have fun!