Are these the best option for travelling around on the Metro?

Going to be flying into Dulles and then taking the bus to West Church Falls (or some combination of those words) station. Then catching the metro to McPherson.
The following day, going to L'Enfant Plaza with trips to the DC Armory, Pentagon area and back before finally going to DCA for a flight. (7 journeys min.)
Might be some other trips if I'm too lazy to walk. Not sure how spread out things are compared to say New York. Use the subway with an umlimted travel pass whilst there and get my money's worth!

Can I buy the SmartTrip cards or passes at any station?