The biggest problem with Washington, DC is getting and getting out. The Metro is probably the easiest way to enter and exit the city, followed by commuter bus.
A couple questions come to mind:
Is this a full-time, year round, 9 to 5 job that requires daily, rush hour commutes to DC? Or, can you select the times when you go to town?
If you can select the commuting hours, you may be able to avoid a lot of the I-495 daily gridlock. When I worked for the Washington Post, for example, I only had to come into the office once a week and I was able to work a deal so that I could arrive at 11 a.m. and leave before 3 p.m.. Under those circumstances you can drive a car.
Will you be living aboard during winter? While I know there are people that do live aboard year round in this part of the world, from everything I've read about their experiences it has been somewhat of a nightmare when we have a bad winter with lots of snow and ice.