In response to all of the above...
Masonry build
150mm cavity
BC understood using the crushed hardcore and seemed ok with it (obviously this is just a call and not an actual decision when it comes to it)
Drive has already had tonnes on it from when we built garage so stoned up really well. Can definitely use some under new terrace to rear of house but I'm sure a lot more than that will come out of the bungalow.
Understood on finish floor height and work back from that, no problems there. FFL will be same as existing bungalow so need to take out what's there down to whatever level we need.