You'll have a blast up there. We went up there from FLa. last summer for a family railfan vacation. I reccomend the Holiday Inn as it is right on the DC-Chicago line across from the Amtrack station and switching yard. You can ask and usually get a trackside room (plenty quiet, however) A lot of activity! The shops are further south of the yard. We did not stop by so I can't advise on them. The WESTERN MARYLAND is a fun ride. Not as senic as I had hoped, however. Neat to watch them turn the engine at Frostburg. Get up hill to the observation deck for great pics.
We discoverd the POTOMAC EAGLE about 30 minutes away in Romney, WVA. and I HIGHLY RECCOMENDED that. Double ended by beautiful older desiels, this train has history and FANTASTIC views. It goes through old farmsteads and then through this beautiful gorge along the river. Usually see eagles, too. We will ride it again next time we are up there - its a too well kept secret.
Feel free to contact me if you need any aditional info.