Thinking a long way ahead does the fibre modem need to be occasionally rebooted like an adsl modem?. Just thinking about its location. At the moment the adsl unit is in the garage next to the master socket and is a bit of a pain to get to.
Well my ONT (original 4 data, 2 Phone port ONT) hasn't been rebooted since I have got Fibre in end of 2016, so no the Modem doesn't need rebooting.
The router (if with BT and using their Smart Hub 2) may / will reboot itself when it needs too do so, but you can use your own router to reduce those reboots.
I would choose a location close to a power socket with at least 2 sockets free (1: ONT, 2: Router) and if you choose BT's new Digital Voice Service it "may" need to be near the Phone Master Socket also.
We chose close to a double power socket in our front room, this made it the easiest for the engineer to install.
The Engineer "might" move your Master Socket if asked, but I would explain what needs to be done / moved to the ISP when ordering it and ask them to put that in the install notes so that the engineer(s) knows about it on arrival to do the install.
Also might be a goo idea to also confirm this information with the engineer(s) at the start of the install.
The Engineer normally knocks before they start to confirm where the ONT will be placed, so be clear and reasonable where you would like it to be placed.
Paul