Eric,
You do not say if you are people willing to share a bed. There are few coaches that can sleep 6 in individual beds, but they do exist.
BW was very right about the Smithsonians. It is about a dozen major museums and then another handful more. Three days is a minimum to even find the majors. Public transportation is very good and parking is problematic and expensive in DC.
Relatives and friends that have come from Europe to tour the US and been surprised by the distances. Please use a mapping program to chart your plan before you commit to anything. It is very easy to be deceived by distances and driving time.
The excursion you have outlined is about 4000Km (2500mi) and 45+ driving hours. You also my not be able to return the coach other than where it was leased. Be sure to check on that.
Also check that the leasee will accept your current license. This varies by state.
Don't abandon the plan, just be sure you can make it all work without killing yourselves.
Matt
