How many days would you allow to see national mall area &Smithsonian museums? How about other must-sees in the area? Would you suggest staying in the Alexandria area separately, or is it reasonable ...
Seriously, even as Boston drivers we don't tackle DC. Aside from traffic, parking is an issue. Cherry Hill will take you in on a bus tour or take you to the Metro, which is what I'd recommend. How long will you need? A lifetime and you won't see it all. Just like Disney, make a list of "must sees" and work from there. Air and Space museum is our favorite.