Respectfully, you would be better served hiring a local Adtran reseller to do this work for you. The 3200 only has a single ethernet interface, so if your comcast actually is point to point, it will be delivered with an ethernet handoff. You will have to use a managed switch and 802.1q tagged sub interfaces to get it into that router. If your comcast connection is just a cablemodem, you could use a gre tunnel over a tagged interface but the software version in the config you posted doesn't have the E suffix, so you won't be able to set up vpn to encrypt the traffic. Your router would need the enhanced feature pack for that.