Plot 1250m², living area 200m², 4-person household

How is the leveling of the property possible (L-bricks etc., what costs approximately)?

That depends on the soil condition. But why level it at all?

The property has not yet been surveyed by us, so we have no exact measurements

For that size, exact measurements are not so important. For the first planning, an excerpt from the geoportal at a scale of 1:250 is sufficient.

especially regarding the height difference.

That is important, though. Very helpful: cross-line or rotary laser for about €130. Cumbersome but cheaper: hose level.

Roughly estimated, the difference between the highest and lowest point of the property is 3-4 meters.

I estimate 2.5 m.

That’s so much about the property and the planned position of the house.

If you are already drawing it in, please do so to scale. Your house in the site plan is about 15m*16m in size and does not maintain the setback area.

that exactly this space from the terrace to the westernmost point of the property is level

Creating a level surface there is certainly no problem. But I fear you mean a horizontal plane and then, given the large area, a lot of earthworks must be moved. To make a statement here, the exact heights of the roads, property corners and planned building corners must be determined.

The main road is quite busy? I would play around with the idea of orienting the house not towards the northern street but along the border with neighbor 77. This way you would have more distance to the main road in front of the main area (living room, terrace).
It would really be interesting to have a map with elevation points. If you want to build without a basement, a non-square house would probably be advisable to reduce the amount of fill needed. The house would then remain more on one elevation level.

An exciting challenge for an architect. In my opinion, the floor plan is rubbish, not worth discussing improvements at all. I’m just saying, 7m2 guest room, main bathroom with cramped layout (everything included) smaller than the kids' bathroom, bedroom with a "pointless" corner just so the square meters don't look quite so tiny ...

From where should the garage be accessed? The distance toward the side street seems too tight to me.

Roughly estimated, there is a difference of 3-4 meters between the highest and lowest points of the property. Here, when it comes to incidental building costs and specifically earthworks, we are pretty much in the dark.

That just calls for a basement or split level.

Number of floors: 2 full floors, no basement Roof shape: hipped roof Style: urban villa

I’m surprised that this is prescribed in the development plan... or are these just your wishes?

For the size, the exact measurements aren’t that important either.

Yes, they are. If you need to accommodate 4-8 overnight guests at once, then this design is out of the question. Representing a guest room as a “living hole” is, in my opinion, wrong.
It would be better, especially with a slope and that need, to think about a basement with a multifunctional room and guest bathroom, maybe actually as a granny flat that the teenagers can use later on.
I don’t even know if a prefabricated house company can manage something like that. Possibly have the planning done by an architect experienced with slopes, and then the execution by a prefabricated house company... although: I believe they only do plain smooth concrete basements, and I don’t see that here.

There are prefabricated house providers who can do that

I am surprised that this is required in the development plan

There is no development plan.

Yes, there is.

Before you raise an objection, please read my posts completely. Of course, exact measurements are important for the floor plan discussion. My comment referred to the property. To clarify, I quoted the OP before that.