Telephone sockets are easy to install and thus theres literally no thought/design that has to go into it. Most new homes do it now.
5-10 Years, work out a budget and stick to it. Cat6a if you can afford it. Cat6 would likely suffice to be honest. Most runs you'll manage 10G anyway.
I'll be honest it's going to be messy so don't go hanging nice new wallpaper because they may need to drill some rather large holes in your walls.
I work for a commercial company and we don't do much domestic work but it can get messy. Especially with insulation in your cavities.
I'd expect them to put a cabinet in the loft, that's what I'd recommend they do it's not ideal but it leads to less mess. Soil pipe boxing in will go right into the loft they can use this. Get them to relocate the BT line or put an extension from it to the loft.
9U Cabinet in loft
24 Way patch panel
4 Way PDU
All cables in the upstairs bedrooms should be able to drop straight down from the loft.
Downstairs wise they can use the soil pipe boxing in as a riser up to the loft.
Consider if you want CCTV, right now is the best time to get it installed.
WiFi too, UniFi is epic.
I haven't read the thread but that's what I'd do.
Hm okay, cheers for the input. I never even considered moving the master socket/BT line. Having it all in the loft would be better as it'd only be a case of dropping it one floor to the first floor where the office is. There'd then be two cables running down one floor again to the living too. I like it...
I'll ask the contractor to consider it and see what price they come out with for both.