If the Train gets in at 7am might be a good time to stop and have a nice breakfast somewhere close by to kill some time...
Pointers... Instead of Route 40 I suggest Route 7/Philidelphia road - There are a few more lights and a reduced speed limit (so if time is of the essence stick to route 40) but 7 has a lot more to look at with a reduction of 'asshatdriversthatspeeddown40'. It is a personal preference and 7 will take you all the way up to port deposit. (I just went there a few weekends ago! It was def. nicer going up 7 than 40, which i took on the way back) A lot of this depends on WHEN you are doing this trip too...
As for in and around DC I haven't really been. Gaithersburg is closer so the new MD rider might have some suggestions for in and around there...