If you're going to have a fire extinguisher system then in the least it'll need to be foam, I hope you're not planning on spraying water at electrics, even if you plan to kill the power to it before you do so. But even then, there is no guarantee you may hit the fire unless you can point the extinguisher in the direction of the fire.
Hopefully you lined your loft walls with fire resistant plasterboard before you skimmed, and you're not using cheap polystyrene insulation!
The FLIR sounds way way overkill. What's your rationale behind that?
It still doesn't explain why you'll be drawing 7kW from the wall. Are you running a rendering setup? or high traffic websites? The only use-case I can think of whereby you'll be drawing such currents constantly is if you're doing some crypto mining
Also, what are your plans for ventilation? 7kW is going to generate a lot of heat.