If I buy the Arris SB8200, will it still integrate with my Xfinity Wi-fi router/modem (Voice and Data Modem Technicolor CGM4140COM) ?
You don't need the 8200 straight cable modem with that device. It already has a cable modem built in to it.
I see it offered on the Xfinity site as an approved retail device, but you have to have a router no matter what right?
Yes. If you were using it alone you would need a separate router if you want to connect multiple devices an WiFi capability.
https://mydeviceinfo.xfinity.com/device/arris-sb8200-587 My main concern is that my voice service will no longer work. I am sort of a novice with networking so do the two devices work in tandem?
The 8200 does not support their phone service.
Will I still have the 2.4 & 5.0 ghz Wi-fi access points? Please forgive my ignorance and explain like you would a newbie... Thanks !!!!!
Again. You would still need a router with a 8200.