Plasterboard in a bathroom: vapourcheck or moisturecheck?

[AdamW]

I am about to open out two rooms into one by removing an existing (and mouldy) stud partition of 1984 vintage. Now, as this will leave a gaping hole I have decided to VERY CAREFULLY remove the two existing artexed ceilings (whilst wearing a good quality respirator, goggles and rigging gloves, then sealing it in heavy duty plastic bags!). Then I would like to install a new ceiling.

Do I need to use "moisturecheck" plasterboard or "vapourcheck"? I am thinking moisturecheck as this sounds beefier.

How easy are these materials to work with? Can I just score and snap like with normal plasterboard? Which side do I skim, assuming they aren't tapered edge?

Does all of the above apply to plasterboarding a stud wall in a bathroom too?

I was thinking about just plasterboarding over the old ceiling and skimming, but as I want to fit downlighters (IP44 rated) the double thickness might scupper the plan. Anyone got any ideas to contribute to that? When I cut out the holes, do I need to treat the exposed plasterboard?

 

[Topper]

. wall areas where fixtures are required ply first them apply the plasterboard. finally finish with multi finish plaster Before tiling apply pva

If you are considering overboarding the ceiling normal gysum 12.50mm plasterboard is fine

downlighters just cut the orginal plasterboard larger than the fitting.
When apply the final board the fitting should clear the orginal board

Best to use vingl silk after