The modem is not designed to go straight into a PC, it typically goes via another router e.g. a Sky Hub, a TalKTalk Router, a BT Hub etc. You can set it up via PPOE, but anyway, link in your TP Link via the WAN port and set up the connection. Should be good to go relatively quickly.
The only comment I have to make is the TP Link Archer D2 is AC750 (750Mbps), the BT SmartHub is AC2600 (2600Mbps) - so the SmartHub has not even just marginal better WiFi, but crazy better WiFi. You are replacing it with a worse device for WiFi.
As far as TP Links go, this has similar WiFi spec to the SmartHub (AC2600):
The point is, the SmartHub is a pretty good router, and if you are going to replace it I would always recommend not choosing a worse spec device, plenty of great devices out there which are more reliable and solid etc, but they are £150+. I personally feel what you are doing is somewhat counter productive. Yes, you gain the media server, but you severely downgrade the WiFi spec.
Edited by ukhardy07 (Sat 30-Dec-17 10:15:55)