Be ware that I-485 is for people adjust the status in U.S. And the AP is for emergency travel.
1. It is safe to leave with all your AP copies.
2. If you change address, they should transfer the case. Why not change to a Boston address?
3.You will get a approval notice by mail. If you sign up on USCIS website, you can get an e-mail notice. You should make an appointment and go to local office for interview, providing 2 photos and filling an applicaiton for the real card.
4.Have a VALID AP before you leave the country.
5.Come back before it expired. But INS might question about your will to live in U.S.