Small JOb - Internal Insulation questions

trinewbie

I have a 1970's semi-d, with poor - Styrofoam type insulation. I need to re-plaster a bedroom, its worthwhile warmboarding/ insulating the external wall of the room at this time.
Questions:
-What type of insulation should I consider: Kingspan Rigid Boad type V Rockwool? What are the pros and cons of each? Which is the easiest to install for a novice DIYer
- Do I need a moisture Barrier?
- Is it best to remove all the old plasterboard, insulate between the batons with rockwool, or can an insulated board go straight on top of existing plasterboard?

I'm hoping to do much of  stripping back and installation myself, and have a plasterer come in to reskim the whole lot when Im done, assume will also need a plumber in to move the rad pipes to allow for the additional space that I will use with the rigid board insulation approach.

Thanks in advance

Calahonda52

No for on top of existing PB: mould issues

yes to screw, with the correct screws, the wb onto the existing battens, assuming you address any surprises that might arise once you strip off all the old pb.
If there is not a horizontal batten at top and bottom of existing, put one in, for fire safety reasons, unless the ceiling pb is fully sealed against the wall.
Mark the position of the uprights on the floor before you slab it up to make screwing the skirting board easier

in passing, are the wall vents fully ducted to inside face of pb and outer layer of clockwork

ps the warm board will be moisture barrier enough