TPlink only sell pairs. Try ebay?

Typical throughput on these is 100-200Mbps so yours is on the low side but it depends on distance, wiring quality and interference. Make sure you plug directly into wall sockets and don't use...

Vodafone issue with their crappy routers. See https://forum.vodafone.co.uk/t5/Broadband-Home-Phone/Vodafone-Home-Broadband-Vodafone-Connect/td-p/2434899/page/19

Get http://uk.tp-link.com/download/TL-WPA8630P-KIT_V1.html#Utility Once you have it open go to the ADVANCED settings for the adaptor that is connected to the router. on the left hand side of the menu...

You can use both together.

Have you logged into them and configured the WiFI? RTFM!