Sealing the plasterboard for the Kitchen

[Nargos]

I have an issue in terms of how to seal the plasterboard in my Kitchen that I am renovating.

I have removed all of the original wallpaper and tiles wile keeping almost all of the plasterboard paper on the wall. In those places where it came away I painted PVA to seal it. I have realised though that I may want to seal the plasterboard behind the wall cabinets and when checking it looked like a bad idea to paint a primer coat on everything as this would let the tiles fall off though it is what I was recommended to do for the wall paper. I also looked at PVA for behind the cabinets but again this looks like a bad idea for the tiles where there would be an interface between the two.

Can someone please tell me what I should do to prepare these walls as I am now lost and can not find any reliable help at B&Q or in books or by reading on-line?

 

[PrenticeBoyofDerry]

No point priming walls to put wall units to, but tiled areas will require priming.
So prime for tiling, whether this is done pre or post wall cabinets, it matters not. Nor does it matter if a little primer ends up behind where the cabinets will be.
Not sure what the issue really is? and why any interface between tiles and units would be an issue, as you cannot tile behind fitted/installed wall units.