ᐅ Remove plaster to install electrical wiring

Hello everyone,
this is a taken-over new build currently in the shell construction phase. The electrician has already been here and plastering has been done.
However, I am missing a few power outlets and power sources for indirect lighting in the bathroom, power at the ceiling for lamps, washing machine/dryer connections, and so on.
How complicated and expensive is this?
For example, the two bathroom walls are each 3 meters (10 feet) wide – do you have to open up all of it?
I am a complete beginner, so sorry in advance for any “basic” questions.
Attached is an example of how I imagine the indirect lighting; is a single cable enough for the whole wall?
Regards, Hana

Well, it’s no use now – since you just took over, you’ll have to adjust the electrical work as much as possible according to your preferences. I would go through everything with the electrician and ask what is feasible and what effort it requires. Some things are easier (for example, installing a light in a niche with a built-up frame in the bathroom) – others are more difficult, like ceiling fixtures – unless the ceiling is or will be suspended. Of course, it also depends on the construction method – timber framing is easier to work with, concrete is a major hassle.
Gerddieter

Wow, okay… that’s already quite revealing. I think the ceilings are dropped (in the open kitchen, I’ve added a photo), but the walls in the bathroom are still unfinished (probably the open kitchen is a bit further along than the bathroom)… is it possible to extend a cable to the next wall (for a mirror with indirect lighting) (see attached photo), for example? Yes, an electrician definitely needs to take a look at it, but thank you very much for your response!