I did an online d/s thingy before. Don't think it really compares anything to having a real life one. Then again, I don't think a d/s relationship (in the idealist sense) is all that practical--hoping it will be exactly like your fantasies can be disappointing. My advice is to try a real life one with someone who is open to your ideas of what you'd like your relationship to be like. My personal stance is that I would never engage in a d/s relationship with someone who I wouldn't have a real life one. I think you should take your time and survey your options and try and get a sense of what you are looking for. Since you're in DC you have a few options of places you can meet people in real life. Check out the Crucible (google), I went there and it was decent I guess. Kinda pricey.

Feel free to message me and I can tell you what it was it like.
Good luck!