OK, from the horse's mouth, so to speak:
1) Yes, there is a minimum speed below which BT won't install fibre, I can't see the reasoning behind this myself.
2) The signal is carried on a twisted pair, not coax as I thought
3) You must have a phone line active to get fibre
4) Not all cabinets for a given exchange will be enabled, initially
5) The BT installation fits a new faceplate to the existing master socket, which filters the VDSL/phone at that point
6) The supplied modem needs a power supply, iow, you need to have a power supply adjacent to the master socket
If I haven't covered anything, let me know and I'll seek out the details.