Remove plaster to install power source

Hello everyone,
this is a taken-over new building in the shell construction phase. The electrician has already been there and plastering has been done.
However, I am missing a few sockets and power sources for indirect lighting in the bathroom, power on the ceiling for lamps, washing machine/dryer connections, and so on.
How complicated and expensive is that?
In the bathroom, for example, the 2 walls are each 3 meters wide, do you have to open everything up then?
I am an absolute layperson, so sorry in advance for “stupid” questions.
Attached is an example of how I imagine the indirect lighting, is one cable enough for the whole wall?
Regards Hana

Yes, it’s no use – if you’ve only just taken over, you’ll have to adjust the electrical work as much as possible to your wishes. I would go through everything with the electrician and ask what is feasible with what effort. Some things are easier (e.g. lighting in a niche with a pre-wall in the bathroom) – others more difficult, e.g. ceiling outlets – unless the ceiling is or will be suspended. Of course, it also depends on the construction method – timber framing is easier, concrete is a huge hassle.
GD

Wow, okay… that’s already quite revealing, I think the ceilings are dropped (in the open kitchen, I added a picture) but in the bathroom the walls are still gray (probably in the living kitchen already a step further than in the bathroom)… can you extend a cable to the next wall (for a mirror with indirect lighting) (picture attached) for example? Yes, definitely an electrician needs to take a look at it, but thanks a lot already for your answer!