plasterboarding behind kitchen base units

Fine idea. even on outside walls this is no bad thing as the units provide an airgap that insulates. Or you can celotex to it as well

Another trick worth pondering, is to put up the units BEFORE you board at all. Then you can infill between cupboards and base with plasterboard or MDF, and achieve sunken sockets without having to chip at the blockwork AND if the wall behind isn't straight, who cares? your new in between bit of wall IS. Likewise you can batten up around and above the cupboards to hide a complete load of bent blockwork very easily.

Personally I would plumb and wire on the surface, add pipe wrappers ,and insulation on outside walls were you can, then make a squared and trued up wood frame using packers to space where the wall is concave..and then infill with MDF or plasterboard as appropriate. Just beware of MDF. It shrinks. But is OK if tiled over and you can tape jonts as well. And it carries loads ad takes screws.

You will also note that IF you arrange trued up battens properly levelled, they will support the high level cupboards as well. This makes putting THOSE up a snap. They just a long screw into the wall

The one downside is that any kitchen refurb will mean a fair bit of making good or ripping out of the studwork..but then what doesn't?. The flip side is rewiring is a piece of piss as is re-plumbing, as all the pipes are surface accessible with the units removed.

I doubt it would be hard work to clip/trunk the cables in a safe zone. However they are probably going to be 50mm from the finished surface (ie back of the cupboards) so they are already safe. Personally I would not be overly worried if they were not in a safe zone behind the cupboards.