Thanks Kenny!
Got my hammer out today, this marks the official start of work!:
The previous owner of the house has left me a little present - anyone want a Flymo? LOL
I think I've pretty much decided that the best way to go is completely insulate and board the entire ceiling as one lot before starting the stud walls etc, so I can get a good airtight seal around the perimeter. So that means I need to run the 2 new ring-mains, network cabling, projector cabling, lighting etc first...Careful planning will be needed!
Ben.