Imo, start with Philly, NYC can be overwhelming solo as a first trip like this. Book ahead on Amtrak and if you sign up for an account they’ll send you deals. It’s a short and easy ride. You can do a day trip or a weekend for a reasonable price. Look up what you want to do and where you want to go first and have a plan. I usually research things to death because I want to walk around confident, and I end up stumbling across something unplanned and have a great experience. Good luck!