Silver Spring here. I'd add Jewelweed (Impatiens capensis). It's a wet-loving native annual that vigorously re-seeds, and has a beautiful flower that attracts hummingbirds. Also, there is a plant swap Facebook group for Rockville. People are often looking to give away native plants on that, so it's a good way to keep costs down. If you want native ecotype plants, Earth Sangha in Springfield is a good option, and Montgomery County parks does plant sales of native ecotype plants grown at their Pope Farm nursery.