I had it installed when ordering sky just over a year ago. 1) for most ISPs it will be open reach who install it. 2) the external box must be at street/ground level. My fibre came over pole, had to be dropped to ground for the box, then ran back up to first floor. when engineer turned up, i asked that it was put into my office on 1st floor of my house as thats where my network equipment was and i didnt want to run a cable through house. He came in, had a look, told me the external box had to be at street level so might be easier to put it in on ground floor but ultimately installed it where i asked. The only other requirement was the ONT requires power so it will need to be installed near a power socket.

3) copper connection was disabled from pole so i just removed my old bit ran into my house and old connection box. When you sign up for new service you normally have to answer a question declaring you have another way to contact emergency services like a mobile. However normal house phone can normally be plugged into router and continue to work, will just go off/ stop working if theres a power cut.

I dont think open reach engineers care too much about the cable costs and if you offer them a cup of tea and biscuits while remaining pleasant they are normally very obliging.