1.give at least one day to Philly, two days will be perfect - one day for sightseeing in downtown area and one day for shopping: They don't have any sales tax on clothing stuff and there are a lot BIG malls in the surrounding areas. I am kind of regretted that I did not shop a lot when I was in Philly.

2. Two to three days in NY. last time when I Stayed in Philly, I took the train to NY, very convinent. It will be difficult and probably expensive to have a parking spot in NY city.

3. two days in DC and on the way to DC you can visit the longwood garden too. it is a 3-hour's drive from Phily to DC.

4. One day to Baltimore if you are interested in this city, close 2-hour's drive from philly.