The TC should plug into the BT hub by ethernet to WAN port..
The TC will be in bridge mode.
You will create a wireless network in the TC.. It is then up to you if you use the same SSID =Network name as the BT Hub or a different name.. the roaming network should work fine.. but sometimes it is easier to just turn off the wireless in the BT Hub and just use the TC.. a bit of trial and error here is the only way to find out.
What do you hope to do with the TC other than wireless network?? It is really not able to store movies etc.. because the ATV is not a media player .. it is a streamer. You need something like a computer or ipad to stream to the ATV. (Unless you JB a Gen1 or Gen2 ATV).