This probably gets asked a million times and is answered already somewhere, but I need to ask to be certain (newbie ya see). Looking for advice on adhesive and grout.

So, complete bathroom refit, some walls are fresh plasterboard, next to the bath and overbath shower its hardi backerboard.

Tiles are porcelain:

Cerdomus.Net

Am I right in thinking I need to prime the plasterboard but not the backerboard? Which adhesive(s) is best suited to my situation?

Floor is the same tiles, just chocolate in colour and will be going over new plywood. Whats the best option for adhesive for the floor?

Finally, grout? I'm not looking for any fancy colours, just plain white will do. Does it have to be any specific grout for near the bath/shower?

Thanks in advance

With plaserboard, if in doubt, prime with an acrylic primer, it won't hurt. Cement based boards do not need to be primed (generally). A single part flexy adhesive will be fine and any flexy grout that is suitable for showers will be fine. BAL Microflex or Ardex F4 with E101 admix is very good.

For the floor, it depends how the floor has been prepared. We need more details to give good advice.

Floor is very thick floorboard, so I can put anything on top of it - plywood, backerboard... I can get 6mm backerboard if it makes it a simpler job?

I like 6mm hardie board used it a few times, Could also try ditra or durobase for the floor