Single-family house layout planning - first planning draft

That’s why the internet is full of used saunas.....which are languishing in musty-gray basements. You really should create a nice area around it and maintain it, otherwise the sauna will just eventually appear for sale online. Often it’s also used as additional storage space for dog food, bags of clothes, etc.....Seen it all already :D

That’s exactly the approach with the sauna on the upper floor, so it could actually be used often since you can’t “go around it” :)

We also didn’t particularly want to get a dog just to then use the sauna as storage for food ;)

hm.., if you look at the bathroom: the tub is 170 x 75? The shower is a 90? And all this planned without installation walls and platforms? The sauna is "in the way". Ok, that's being criticized. But look at the rest: do you want to shower in a 90 glass cabin? Bathe in a space-saving tub in a two-room apartment? Without a platform for a sponge or something? If you draw everything nicely, you'll realize that the sauna also ruins the room here – just as I already criticized with the pantry. I'll say it as it is: an architect or someone who plans rooms in houses hasn't looked at this yet. And if we want to extend the list of interesting faux pas: door to the office ... and the start of the basement stairs is blocked by a wall. The door is incorrectly placed by you. But that's what you're here for, to eliminate the mistakes :)

Thank you for the (direct and unvarnished) input :) we need that! :) We haven’t yet taken any planning influence on the bathroom. We really want to draw everything nicely as we imagine it. The shower should – as it currently is with us – rather be a nice walk-in shower. The faux pas with the door and the basement stair entrance we also have to improve! Feel free to give more hints ;)

I like your use of the term "space" instead of "dead space" :) :)

I also like a large entrance hall/corridor because, in my experience, it often happens that, depending on who and how many people come into the house, the "chatting" often already begins in the hallway and "people" often don’t want to stop even when saying goodbye. It’s simply nice to have "space" there. In a private house, neighbors who just want to borrow something briefly or similar often drop by, so "people" don’t invite them into the living room but still enjoy a little chat in the hallway.

however, we didn’t just want a “standardized”, square townhouse with a hipped roof but wanted to add a bit more personal touch with the bay window on the ground floor.

The best joke here! I laughed myself silly when I read that sentence. Just to explain: personal touch is not what everyone is building right now. And the so kindly called substitute villa by user 11 (I loooove this expression!) with a bay window is currently probably one of the most popular building styles. For the beloved substitute villa, the home office then just has to go into the basement. You have a rectangular NOT square building plot, so why does a square coffee grinder house have to be placed there? Before I repeat most of the suggestions here, I would like to suggest moving away from the square as a floor plan and considering a rectangle. That is easier to divide, and I wouldn’t be surprised if you can then fit the home office well into the ground floor and still find a niche for a small sauna upstairs. Or is your heart inseparably attached to this (boring, unimaginative, built a hundred times over and certainly not individual) townhouse design?

And the so nicely called Anstattvilla by the 11th (I loooove this expression!) with a bay window is currently probably one of the most popular building styles.
[...] You have a rectangular NOT square building plot, so why must a square coffee grinder house be placed there?

I am already glad if it is not immediately exaggerated into a Willah (with gangsta gold chains and "only real when leased" fancy noble cars) ;-)
By the way, the Hanseatic coffee grinder is the honorable traditional form of what the KfW cube desecrates with its flimsy plagiarism :-)