Leveling uneven kitchen walls for porcelain tiling

[poiupp]

I will be tiling with 60*30 procelain tiles. They weight about 3.57kg each which is about 20.6kg/sqm
The wall is not flat and it's plastered. When ripping the current tiles off, some of the plaster also came off and when doing the "coin test" I can feel that some bit of plaster are not sound.
Considering all this I think that tiling over the existing plaster is a no go. How can I solve the situation?
I was thinking about doing the following:

1) in the area that will be tiled, chisel away the unsound plaster exposing the sort of mortar underneat. Leave everything as is where I will not be tiling... the kitchen units will cover that area anyway
2) install sheets of 6mm hardiebacker in the recessed areas where I will be tiling
3) install all the kitchen units and then tile over the hardiebacker
Do you think this would work? Any other idea?

I know I could just use plasterboard instead of the hardiebacker but it would be ticker and I don't know if that thickness would be excessive. Any advice?

Could I just try skimming the wall with some cheap-ish rapid set tile adhesive? Or will it build too much adhesive on the wall considering that I then have to use a 10mm layer for the tiles?

 

[Dave]

Hi. Can you provide pics of said areas and the state of the wall ?

 

[poiupp]

Here are a couple of pictures.
The remaining bits of the old kitchen will be gone by end of today, but I won't be moving any copper pipe or any of the electrics, so I can't really bring the whole wall back to bricks. I thought that my best bets are to either:
-somehow flatten by skimming, but I can't do it with plaster because of the tiles weight issue AND I don't intend to wait 3/4 weeks for it to dry. What product could I use for that?
-create a recess just where the tiles are going to be and add a layer of hardieback just there (however, I would probably need to put some sort of leveling compound behind it because there's no way I can create a flat and uniform recess. Again... what product could I use for that?