Floor plan design single-family house approx. 230 sqm plus basement

DIN A4 is a good keyword. I strongly advise you to draw your floor plan ideas by hand. Then it should become noticeably clear to you much faster that you lack a sense of dimensions and are planning a correspondingly unnoticed oversized house. Your draft has no characteristics of a house where a family allows itself generous spaces. Rather, it looks as if someone's scale got off. Maybe you better take DIN A5, because on DIN A4 you should actually be able to fit both floors.

Can you describe that in more detail? What exactly is misdimensioned? Where do you see problems? I would be grateful if you could illustrate it with examples.

That alone should be (even if the numbers were realistic) an amber alert: that’s well under ten percent "reserve" until the knockout blow. You would need an architect whose " approved" seal would have five stars ;-)

Without everything here being "bad": definitely start all over again from scratch. And don’t forget the site plan. Even on a 2,000 sqm Ponderosa, it doesn’t not matter where the house is located.

By the way: 230 sqm is a size category for double earners both above the assessment limit!

Let the realization be my concern.
Furthermore, I have to disagree with you: it does not have to be that both are above the assessment limit.

Site plan with elevation details are minimal requirements for an assessment.

Aerial view of the surroundings and the development plan would also help.

The house can be done more efficiently.

I will provide the site plan later. The plot is at around 250m.

Can you say what you think can be done more efficiently? That is exactly what I want to find out here.

I mean the different heights on the property, street, etc.

160 m2 instead of 230 m2.

Do you already have the property?

Plans either with north at the top or draw a north arrow.

The realization is my concern.

You estimate the house construction costs at €650,000. How do you arrive at that estimate? Do you already have concrete offers? For a rough estimate, this forum assumes about €3,000/m². Additionally, you want a basement, which (if it is not developed as a living basement) can be calculated at about €1,000/m². With 230m² of living space and 115m² of basement, using these values you already get 3000*230 + 1000*115 = €805,000. That exceeds your stated budget. This is what people are trying to convey to you. There are also additional costs such as exterior landscaping, fittings, etc...

It's less about whether I can afford it or not. It's about the planning

Ok. Then just say that it can also be €900,000 for the house because you have the buffer. Otherwise, there is no point in discussing if the project is dead anyway before the building application is submitted.

I mean the different heights on the property, street, etc. 160 m2 instead of 230 m2. Do you already have the property? Plans either with north at the top or draw a north arrow.

The property has an 8% slope (falls from east to west), the street runs the same way. The property has a frontage of about 37m. From the street, the left and right property boundaries run parallel for the first 30m. From there, the right boundary runs to the left. The left boundary is a continuous straight line. At the end of the property, the two boundaries "meet" at a distance of 12m.