Hello Sew History,
My apologies for not replying sooner, I had thought I had sent one and noticed I had not.
Yes, Philadelphia has a lot of great history centrally located. Yes, Old City is an area right next to Independence Hall and the Independence National Historic Park. It’s possible to spend a few days walking around and seeing everything (or an afternoon just walking around without going into every building/museum), so you can choose what you might like best and see what your schedule allows for.
It should be a great time, it is exciting you will be visiting!