I've been having problems with my internet when multiple people are using it so I am going to get a router with Qos, possibly a TP-link Archer C1200. How would I set this up? Will I still use my current bt homehub 5 as a modem then connect the router to it?
No, the HH5 doesn't have a modem only mode. Just ensure you get a VDSL modem/router rather than ADSL modem/router or plain router. The TP Link models have a quick setup function that just requires you to enter the username and password of the service. This is a generic firstname.lastname@example.org and bt
The Archer C1200 is just a router and isn't suitable.
tplink AC1200 if you want dual band