Do I need to set up my new router with the old info, or is it on Xfinity servers?
The only thing that really changed when I replaced my XB3 was the SSID/password. You can change it to your old SSID/password if you want to so that all your wifi devices won't have to be changed:
This article might be helpful for activating your new Gateway using the xFi App
Please let me know if you have any questions