"To ensure it works, it needs two way coms of some sort, i.e. turn on boiler, and a reply OK turning on boiler, there are cheaper methods, like if no signal received in 30 minutes assume battery is flat on thermostat and turn off boiler"
really!
Hire a QS and have the job calculated for materials and schedules. This will cost you a few £00 but is worth every penny
Then you purchase the materials to be available as per building schedule. This protects you and ensures that the contractor is not cashflow financing your project.
The...
6 or 12mm cement board...adds mass, thermal insulation and sound reducing properties...oh yeah, and they are very difficult to set a light...very difficult