Thanks for the advice. We have such large luggage because we are flying from BWI to Buffalo and spending a few days in Toronto & Niagara Falls. Since we are arriving on Sunday afternoon would it be reasonable to take the bus to the metro station and then on to Rosslyn? I assume it would not be nearly as crowded as during a weekday. We could then take the Super Shuttle back to the airport on Wednesday. Does that seem like a more reasonable plan with our large luggage?

Your transport plan makes sense, though your luggage still doesn't.

Many of us are capable of traveling for weeks at a time with just a carryon. I can't imagine traveling with a 27-inch suitcase unless I was carrying my Iditarod equipment, or a wedding dress, or perhaps relocating to a new city. I'll admit that the carryon-only is extreme, but I think you'll find very few seasoned travelers who even own anything 27 inches.