Floor plan single-family house approx. 180 sqm

The floor plan came about as follows. From the beginning, we wanted to build a classic city villa. To get a sense of space for this, we looked at some houses in the model house park Kaarst ( ). We did not like the city villa placed there. We also did not like the other houses in their design, but we still looked at them all once. In doing so, the V480 Edition II caught our eye. The most recently established floor plan is based on this floor plan. We especially liked the open living area. I think we got a bit carried away here and wanted to implement this at all costs without noticing that it would end in a disaster. You opened our eyes here. So back to the roots...

No, towards the architect (not draftsman)! Thanks for explaining the disaster development. However, unfortunately, I do not have the impression that you have now reined yourselves in :-(
An Edition 480 II is a knee wall house with an effective knee wall height of about 190 cm, and is therefore basically quite suitable to serve as inspiration for a classic city villa (with eaves height at the upper floor ceiling). However, the similarity to your variation is too faint, so it is rather advisable to start from a blank sheet. With your planning sensibility (being laymen is no shame), you should urgently go to professionals. A trainee nurse has no business in the operating room. You spend large suitcases full of (mostly only borrowed) money on the house, so do not take for planning anyone who understands it only a tiny bit less badly than you yourselves.

And do not make disruptive specifications. A staircase in a floor plan is more than just the decider, it is downright THE DECIDER!!!
– so never take the muzzle off this Hannibal Lecter!

In the first floor plan, we would also have had to manage with a smaller garage (3.85 m). [...] However, if we were to place the garage on the other side, we would have to keep 1 m distance to the property boundary. Thus, this option is dead.

You notice the contradiction yourself, right? Three meters eighty-five instead of six meter garage width on the left side of the plan would be okay, but five meters on the right side of the plan would be too little *scratches head*

Would your development plan or your parking space regulations really allow any garage size, and would an uncovered parking space also have to be fully within the building envelope? – check that or name (without link!!!) the development plan.

Overall, get away from wishful thinking and into reasonable basic analysis. You really urgently need a clean performance phase 1 and 2 (which never exist in a draftsman’s "planning"), so that every waiver of an architect would keep the course towards disaster. Imagine you had not been bothered by the oddly shaped second children’s room and you had considered the first draft shown ready for construction. Then you would have built excess square meters worth around sixty thousand euros – which is, again: WITHOUT any return! – about double an architect’s fee with full support* (which is money well spent and therefore fully pays off).

*) Google with quotation marks: "A house building schedule, also for you: the HOAI phase model!". This source also explains how to prevent the upper floor from being limited to the least evil

We did not create the floor plan ourselves. Therefore, I have no influence on the furnishing.

That is clear. Generally, a house design is created by an architect or their draftsman. Then there are the measurements, and the builder, client, and future resident draw their own needs, furniture, etc., to scale in this plan. One should not be misled by 70s templates or other placeholders where a sofa is 1.80 meters wide.

I would throw in the Viebrockhaus Maxime 420 II as a house option. A real city villa that, despite its 160 m2, offers almost as much space as your current floor plan because there are no unnecessary corners/niches/hallways. You save 60,000 euros and still have plenty of space for yourselves.

I would suggest the Viebrockhaus Maxime 420 II as a house.

Yes, that would practically be the functionally proven version of what the OP showed in post #19.

But without this unnecessarily long corridor on the upper floor. So much more efficient use of space.

But without this unnecessarily long hallway on the upper floor. So much more efficient use of space.

I said, "functionally proven variant." Catalog houses are usually quite well optimized in terms of circulation areas.