1 week + 1 day RV roadtrip from New York City

I would like input on a roadtrip I'm planning to take starting monday July 1st and ending July 9th (1 week + 1 day). I'm renting an RV in NY (Cruise America in Roslyn not far from La Guardia airport).
I haven't put all the details down yet but my intial plan (which is changeable btw) is that the rough outline of the trip would be a triangle between pickup in NY - Niagara Falls - Washington DC - back to same point in NY. Not necessarily driven in that order.

During the trip (given that this is the outline I will end up with) I hope to cover:
- Some nature for halfday walks/hikes (Catskills/Finger lakes etc?) Where?
- Niagara Falls with MAYBE a SHORT drive into Canada. Where in Canada?
- Some amish area/market. Where?
- Some nice historic sites like e.g. Civil War sites or colonial related (Gettysburg?). Where?
- Washington DC with main attractions and museums (Smithsonian?).
- Some nice shopping outlet area. I read about a place without tax with good outlets in the southern area of my suggested route.
- Maybe cover some parts of the coast south of NY/east of DC (e.g. Jersey Shore, Atlantic City, Chesapeake)


It's easy to plot just any route (i.e. highways) on the map but I don't know what I'm missing if I'm taking short detours and jump off the highways.
Another question is if I should completely rethink the whole route and choose another?

4th of July will be in the middle of that week. Any particular stops that might be good to stop for that celebration (e.g. DC)?

Welcome aboard the RoadTrip America Forums!

For some general background reading with a number of suggestions and links, check out this discussion, as well as this one.

I am personally a big fan of the Eastern Shore of Maryland as well as Annapolis. From Washington you could easily visit Maryland's capitol, cross the Bay Bridge, see St. Michaels, and then work your way up through Chestertown, Elkton, and Fair Hill into Pennsylvania Dutch country and Gettysburg.

Be sure to tell the RV rental firm up front that you plan to take the vehicle into Canada as they may have to provide you with some additional paperwork.

AZBuck