Install a window afterwards?

According to the construction service description, it should only be Ytong with plaster, yes. Inside we would have to redo the wall anyway, since the old tile backsplash has to come off, so I would plan for that accordingly.

Unfortunately, our house has hardly any windows on the south side, and that is really a shame. "A bit more light" would completely change the whole feeling of the room in this case. Currently, the short side of the L-shaped kitchen is partly under the only window, and under the rest of the window is the dining area. But that is totally cramped. Therefore, the dining area there should have more space. Then the kitchen L would be completely without a window – I would find that very unfortunate. If it is somehow feasible, that would be more important to me than other "frills" on the kitchen.

Right, we have shutters everywhere, so that should be included there as well. I would also find it very nice to integrate the countertop. Actually, the window could only be placed at the spot where the water/sewage lines are located, and I do not want to have them moved. We don’t have a basement underneath, that would be a huge mess, and I also do not want to touch the floor. I was thinking of a solution with a fixed lower element.

I will definitely do that.

Yes, that’s roughly how I had imagined it too.

What kind of splashes reach from the height of a sink all the way to the window? And if they do, it's just water, right?

So if you're already installing a window, I wouldn't make it any narrower; after all, it's primarily about more light, and I think you shouldn't reduce the window area like that.

And, .. sometimes it is also nicer to have the work surface extend into the window reveal at the window and to have the sink immediately to the right or left. This way, even in a "normal" single-wall kitchen, you have a piece of surface that is deeper than 60 cm. So my recommendation is definitely to plan the kitchen first and then break the window into the wall.

Ok, without exterior insulation and if the interior is going to be replastered anyway, then the additional effort is limited. A roller shutter of course costs extra and might need a new cable. But if it's the south side, it can't be done without a roller shutter. We have no windows on the south side at all and are glad about it; otherwise, I would have the shutter down all summer because it would be too warm otherwise. We ordered a new kitchen and had the interior replastered and we knew there used to be a window in our kitchen on the south side. The lintel was even already there, but we consciously decided against reactivating it. That is clearly a matter of taste.

What splashes come up at the height of a sink reaching to the window? And if so, that's just water, right? So if you install a window anyway, I wouldn't make it narrower; it's mainly about more light and you shouldn't reduce the window area like that, in my opinion.

I will not be able to move the sink, and it is the only possible position for a window. Unless I do not install the oven high up, but we would very much like that.