Single-family house 160m2 with basement, 500m2 plot

Personally, I don’t like guest WCs without natural light at all, I would probably only reduce its size and keep it in the original location. You still gain the space for the wardrobe, and in my opinion, it’s even better further back/upstairs, because when entering you take two steps inside first and don’t stand right in front of the front door in the way for other visitors. You just have to decide whether natural light is more important to you in the wardrobe or the WC. It is definitely doable.

Edit: if you want to omit the window entirely, the situation is of course different.

That would be a good way to make a window possible if the bathroom is moved downward according to the plan. Light can come into the hallway through the front door plus a side panel.

I welcome every omitted garage connection door, but what do you want with 20 sqm foyer in front of the toilet? - don't forget that a basement bathroom means a lifting system. The strategic intention of your current wave of changes is not clear to me.

Is it total nonsense to build a small guest WC without a shower and without a window?

I find it tolerable in a terraced house or something like that. Still, I have to honestly say that it annoys me when I have to turn on the light in the guest WC due to lack of daylight (so in the evening or in winter). It is indeed nice and comfortable when there is light coming through a window. Apart from that, a toilet and sink right by the door is very valuable when you are working in the garden or in the yard. To be honest, I don’t really see your problem now (except that you see many things as too complicated).

Guest WC without light is completely fine, but of course a WC WITH window is just as good. You don't necessarily need a controlled residential ventilation system for that, just a regular bathroom fan. As the two words say: "Guest" + WC, so a rarely and only very briefly used room, like maybe a storage room. That it is present is definitely a YES for that, but that would be it for me if I could gain even a small advantage elsewhere because of it. I absolutely agree with ; it looks like the planning is only halfway done with this emptiness in the huge hallway; like in a factory owner's villa. I still see the staircase elsewhere. It divides this already not very wide area in an unpleasant way. I think you should simply redesign this ground floor layout completely (have it redone!); it would be a shame if you let yourself be pushed into somewhere there. Shower in the basement near office/guest is an absolute must in my opinion, even if a lifting system has to be installed; that's not rocket science but I wouldn't like the basement without a shower/WC at all. That way you could also use it anytime almost as a separate unit, without having to come into your private living area (guest would otherwise have to go from the basement to the upper floor to shower). Your kids would cough if he messed up one of the 3 small sinks—

I find it tolerable in a terraced house or something like that. Nevertheless, I have to honestly say that it annoys me when I have to turn on the light in the guest toilet due to lack of daylight (so in the evening or winter). It is indeed nice and comfortable to have light through the window. Apart from that, a toilet and sink right at the door is very valuable when working in the garden or yard. To be honest, I don’t really recognize your problem (except that you see many things as too complicated)

Surely it is better and more comfortable to have a window in the guest toilet, also at the house entrance for all imaginable cases. However, as soon as this would restrict another important function, the window in the guest toilet would probably be the first thing on the chopping block. I don’t believe that sees it as too complicated. It is complicated to build your own house and avoid mistakes. I really believe that an interior designer or architect (even someone who is currently in advanced studies in this field) can resolve this situation in multiple ways. rightly wants it to be nice but I think the planner does not fit!!!