From memory it was 6mm (5.6) for the main panel and 12mm for both the halo and spacer.
I glued the original ceiling fasteners in to the metalwork and attached the panels to them with countersunk screws. The fabric covers all the fasteners which looks nice but is obviously a bit of a disaster if you need to get access...
I have the rear 4 spots connected to the interior light circuit but they can be switched independently via a relay. The front pair are currently just on switches either side for the passengers. Eventually, when I get some more relays all 6 will be switchable between the interior circuit and leisure battery.
The halo gap has an led strip which is purely switched.
Everything is currently powered via the starter battery but only energised with the ignition on so no flat battery. Once my leisure battery is in I'll swap over to this instead.
More pictures here.