I am not sure whether I need Extender or Powerline adaptor - is there a device that supports both?  is the Deco product just a range extender product?

I have a BT Hub 6 router and no existing TP-Link devices.  I am looking for the right product to extend my internet access to my SummerHouse (which shares Live & Neutral ring with main house but has its own earth rod for Earth).  I want to use WiFi connections in the SummerHouse.  I want the Network ID and PW data to be the same in the main house (BT Hub 6) and in the SummerHouse.  Will theTL-WPA8631P kit (2 plug in modules) do all these things without having the buy additional units?  

My existing BT Router reports 27Mbps download speeds at the router outlet.  What speeds should I expect to be able to achieve in the SummerHouse using theTL-WPA8631P? Forgive my ignorance but I see figures like 300mbps, 600mpbs and 1200mbps for the various TP-Link products but dont understand how these numbers relate to the internet download performance I can achieve when connected to my existing BTHub6 via the TP-Link device?

At a later date I may want to add another "repeater" in my upstairs office to improve the wifi signal/speed there.  Would theTL-WPA8631P support this and what other TP-Link units would I have to purchase to achieve this?  

Is there another TP-Link kit that would achieve my needs at a lower price than theTL-WPA8631P?