No. You don't need a Realtor.
If you don't use a Realtor, you should have a lawyer. Even if you do use a Realtor, a lawyer is advisable.
By the way, there's lots of rent-to-own activity in the D.C. area, especially in P.G. county. If that's the way you want to go, you shouldn't have much problem finding a property.
Hope that helps.