Congrats on your new rig and
I know how badly we always want that first trip to go well but don't get discouraged if something goes wrong. Our reactions to problems are often worse than the problems themselves so do your planning and hope for the best. You'll have a great time.
We love Cherry Hill too. We were there before the express bus was running from the park to the subway station and found that driving to the subway was MUCH nicer for us. With an express bus it might not be so bad. Don't drive to the mall.
The most memorable thing we did was take a guided Segway tour of DC. Easy to learn to ride them and it was a blast. My DW is about as far from being athletic and adventurous as they come and she did well on the Segway and wants to do it again.
After DC we found Gettysburg to be a facinating stop.
Have fun and be safe.