Advice please-BT Master socket, D6300 and WN2500 extender

Dear All

I hope this is the right place for this question, it was difficult to pigeon hole. OK here is my problem. I am in the UK so phone wiring and sockets all from BT. Like most my BT master socket is downstairs in the hall and my computer and office with a builder wired extension is one floor above.

I had some speed issues with the broadband... BT Special Fault team were really good today and together with TalkTalk Business they have put me on a better line etc. However the problem is this. If a speed test is run from the master socket downstairs I get 12mb. From the office i get 6mb, Obviously i cannot place the router downstairs as I have wired connections but I had an idea which is what I wanted to ask.

I have a new Netgear D6300 router. With a wire I have connected:
- PC
- Laptop
- Awaya IP 4610 phone
- Sonos Bridge
- ReadyNAS Duo v1
- HP Printer 6500A PLUS

Yes thats six things but the phone and Sonos has pass throughs so all hard wired. I then have two Ipads, two iPhones, two Sky wireless boxes and a PS3 on the wifi as well as the Sonos play 5s and 3s.

What I was thinking was, and would this work. If I move the D6300 downstairs to the master socket and then bought a WN2500RP range extender for the office which has LAN sockets.

So my questions are for you all:

1) If I did that move and purchase, would I connect the wired componants into the WN2500RP? Would that work?
2) would they then be connected wirelessly and have dropout etc or would it work just as before, ie. like a wired router?
3) as i would get 12mb from the socket, would that work over the wireless link to the WN2500RP?
4) could i get the BT master socket moved?

Thanks a million in advance.
Best
cjd