I'm on Sky fibre pro unlimited which is a little different to BT but you will get an openreach modem and a HH.
Ideally the OR modem sits at the master socket but can be resited with an extender kit. Ask the OR engineer.
With the aid of a long enough ethernet cable the HH can be sited anywhere you want, within reason.
Yes you can replace the HH with your own router quite easily or so I have been led to believe.
I hope your install goes without a hitch. With the cab so close you should get top speeds.
Enjoy