From my experience, can't really assume that OR or their sub-contractors will be able or even willing to try to get the fibre run to the location of your existing POTS master socket, in my case the old copper line was UG fed but DIG, ie. armoured cable, not in trunking so no attempt to follow that routing with the fibre could be made.
At my son & daughters properties, also copper UG fed but later builds and in trunking, OR sub-contractors failed in both cases to run the fibre through to the master sockets due to blockages/trunking collapse and settled for a convenient "hole in the wall" entry.
I settled for an ethernet cable run between the ONT and where I wished the router to be which in my case was quite easy to achieve and conceal, timber framed bungalow.
You mentioned UPS backup requirement, presumably for ONT & router?
I already used a central UPS unit so decided to incorporate a PoE feed to the ONT which of course also powers the router, details here in this rather long saga of my FTTP migration experience.
https://forum.kitz.co.uk/index.php/topic,26792.msg451455.html#msg451455To be honest, it hadn't occured to me to extend the fibre at the time of my installation, don't remember fibre extension kits being available then, an ethernet cable run was the easiest option for me at the time, no issues close to 3 years on FTTP.
FTTP installation on the day will very much depend on the mood & competency of the attending engineer whether OR or sub-contractor, from my limited experience any pre-install preparation by the customer provided it's to an acceptable standard is usually appreciated.
Good luck with the FTTP migration when it comes around, hope it goes well.