Regarding the Poe museum: Friday afternoon is fine with me. It would be helpful to me if we could meet at the hotel or Troll Cave, rather than at the museum; and if Succubus and I could ride with someone else at that point to the museum.
Regarding DC: I recommend, if you go, park at a metro station and take that downtown. The stop you want is helpfully called "Smithsonian". It's in the middle of the Mall, walking distance to nearly everything you'll want to see, and you can get to it via the orange and the blue lines. It beats trying to park downtown, in my opinion.
Hope that is helpful.