I've done the trip a bunch of times and echo the sentiment to leave early and not to worry too much about the currents. Keep in mind that the Delaware is shaped like a giant funnel. Thus, as you transit south, the effect of the current becomes less and less noticeable. Of course, the opposite is true heading back, but the worst of it - from the Nuc plant to Ches City is in really protected water, and pleasant (I like the canal).
Do NOT, repeat, NOT anchor in the vicinity of the Salem Nuc plant. Many years ago, we anchored there late one night in an effort to get an early jump the next morning. The current is wicked (it's near the bottom of the "funnel") and we wrapped our anchor line around the keel and eventually lost it at 0300. Good thing that we'd established an anchor watch and weren't cast adrift while sleeping. Instead of setting the second anchor (the primary parted while we were preparing the second), we set sail and sailed the rest of the night to Cape May.
The Delaware River part of the trip isn't the most fascinating, but with Cape May as the prize, it's ok. Good luck.
If you do anchor near the plant and find our anchor, PM me.