Business casual and business are both fine!
Hummingbird is close to the waterfront, about a ten-minute walk from the Church and an even quicker Uber.
Street parking is available throughout Old Town but can sometimes be difficult to find on the weekends. There are several garages in the area, the garage at 111 S. Pitt Street, Alexandria, VA 22314 being the closest to the Church.
Sheraton Old Town, Hilton Old Town, Hampton Old Town, and the Heron are all good options. Indigo Hotel is also nice and Hummingbird, the reception location, is located there.