I lived in the DC area for roughly 20 years. MoCo, primarily Takoma Park & Silver Spring.

NYC is always a good time.

You mentioned Harrisburg. I'm not sure you can get away with 3 days there (unless you go right now for the PA Farm Show, which, if you've never been to it, GO.)

THAT being said, add in a Carlisle day (w/ a nice chill few hours around the lake in nearby Boiling Springs), and/or a nature day at either Kings Gap or Pine Grove Furnace, and you've got a 3-day weekend. (Also, you mentioned Penn's Cave, which is definitely cool, but there's also Indian Echo Caverns outside of Harrisburg/Hershey.)

But, yeah, if you can go this coming weekend, and you don't mind crowds (COVID is still out there; stay protected), I'd recommend doing the Farm Show on Friday, Harrisburg on Saturday, and spending some time checking out the view & hiking a bit at Kings Gap on Sunday before heading back (or switch the Sat & Sun around depending on weather).