Agree with all posts that this is totally doable and very worthwhile, especially if you've never been here before.
In addition to the DC options mentioned, Old Town Alexandria (founded in 1749) is a 5 minute cab ride or 2 metro stops south of DCA on the Blue/Yellow lines. Lots of great walking spots, museums, etc. and good places for a casual lunch. Have fun!
Originally Posted by
travelingdrsuz
Book a window seat too. This is one of the better views arriving and leaving. )
Totally agree. Specifically - you'll want to be on the left side (A seat) on arrival, and the right (F seat) on departure for the best views.