I am currently in the process of having my house re-wired and will be running cat5e cables to each of the bedrooms plus the living room. For each bedroom I will run 3/4 cables to each bedroom and 4/5 cables to the living room. The reason for this is because if a cable breaks for whatever reason you have spares that you can just hook up without pulling all the floors up to re-run the cables, Plus If I intend to run HDMI over ethernet it requires 2 cables to run at full 1080p. If you are doing this from scratch do you have a central location you can terminate all the cables at? Mine will be under my stairs and I am having the phone master socket moved there. I will then connect my modem etc to a hub under the stairs and have this as a central location for all electronics such as a NAS box I will be installing and my media center/sky box will go under here with some IR repeaters for the remotes.
Yes, I would (and have) got all my wiring returning to a central point. I installed a small 8u (iirc) cabinet in a storage cupboard upstairs with a 48 port patch panel and 24 port switch. Once we switch to fibre my router will also be in there with the separate fibre modem located at the phone socket.
In regard to your phone socket, I would image the electrician is installing a phone extension rather than moving the master socket as this would require BT Openreach to be involved. What i personally have done is connected my router at the master socket with a cat5e running from there to my 24 port switch in my cab. That way the phone cable distance is kept to a minimum and ensure i achieve maximum ADSL sync speeds. Your cat5e wiring can also be used to provide phone extensions around the property if required.
Always install more data points than you think you will need...trust me they soon go. Also for your HDMI over cat5e, you wont be able to terminate these into cat5e faceplate's. The cable will need to be terminated directly into a plug otherwise the losses caused by the additional connections can and do cause signal drop outs and sync issues. (Personal experience)
Last point, make sure you install plenty of double sockets under the stairs to power your equipment. I would suggest at a minimum 4 x double sockets as you will have quite a lot of equipment to plug in. Just reading your post suggests you will have:
Router
Switch
NAS
HTPC
Sky
Oh, and last last point don't forget to ensure you install adequate amounts of WF100 (aerial/sat cable) to the under stairs cupboard for your Sky LNB feeds, aerial feed, DAB/FM aerial possibly?, as well as every room you wish to have a TV point
