On Friday, 29 May 2020 18:38:15 UTC+1, tim... wrote:
3) add an Ethernet socket on the wall by the router, connected to another
one in the office, plug the router into one, and the computer into the
other.
If I install sockets on the wall, are they easy to wire up? How do I handle
Rx/Tx crossover (or don't I need to?)

You don't, that's handled by Ethernet - and most adapters now handle crossovers if they occur inadvertently.

I have read that there are restrictions on bending the cable
Will I be able to get around the 90 degree corner as I go up the side of a
wall and then turn to go along the ceiling, all inside trucking? Will I
have to go around that corner outside trucking to avoid bending the cable
too much?

Probably not.

Don't use CCA / aluminium cable.

Owain