In terms of the ceiling pendant, for many people the correct answer is "ask the wife".
In terms of drilling holes, the real oldies got excited when a Rawl Drill came along instead of the old 'hammer and rotate' method...
The correct jointing kit is eg https://www.ebay.co.uk/itm/233823894403
The same seller has 2m of drop wire if you do need extra length (in which case you'd probably need 2 of the joint kits too)
https://www.ebay.co.uk/itm/235831824586
If you're desperate buy an ethernet patch cable and cut that...
It must be an unswitched socket.
Boilers require double-pole isolation and some switched sockets are only single-pole. Someone could switch off the switch and the boiler would not be completely isolated if still plugged in.
Gas rules / boiler instructions usually.
You don't need to go full fibre to have your voice 'line' switched to Digital Voice (Voice over IP).
If you change supplier, or possibly even a new fixed term contract with existing supplier, this can trigger a migration to Digital Voice over VDSL (fibre to the cabinet).
BT are wanting everyone...
Boilers require Double Pole isolation so must be used with a plug and an UNSWITCHED socket, or with a FCU.
Plugging into a switched socket is not permitted, as not all switched sockets are DP switched.
This might be in Gas Safety regs rather than Electrical regs, but is required.
Kitchen unit fixing rails eg
https://www.tcfixings.co.uk/product/cabinet-hanger-wall-rail-27mm-x-2032mm/13864
together with suitable wallplugs as mentioned.
No, you drill a small hole in the decorative rose and feed the cables through from above. Then affix the light fitting onto (below) that.
If it won't sit solidly over the flower effect you will need a decorative rose with a larger flat centre, or a different fitting.