Floor plan of a single-family house without a basement, 3 children's rooms, and an office

I would leave out the pantry entirely, you don't need something like that. The food goes into the (mehr als reichlich vorhandenen) kitchen cabinets and the kitchen would also have enough space for a spacious peninsula with a bar/counter.

Exactly, that is the building envelope. The ridge direction is predetermined. Therefore, I wouldn’t know how we could pave less if we still want to drive into the garage...

Well, you yourself write that only one car needs a garage space. Also, you don’t have to use the entire building envelope.
And I wrote that more brainpower should be used… there can also be a window area on the west side…

The predetermined building envelopes are restrictive. You have to set priorities: if you want your bedroom at the entrance and dirt area and the kitchen in the north, then that’s how it is. Most prefer south and west-facing sun in living areas and would rather zone a long, stretched open space with design elements than give up sun and light.

however, then the kitchen, dining room, and living room would be in one line.

we have already obtained 4 different turnkey offers, all under 500,000 euros.

.., where we always get stuck on the topic “turnkey,” which can mean everything and nothing.
Does the price then include the elaborate double garage with roof and finishing? If I were you, I would take a look at the construction service description to see what is really offered for the price… otherwise it will be cheap, which is not an advantage.

The house will probably be about 8.5 m x 12.5 m in size. So we are already almost at the limit here. Unfortunately, it can’t be much bigger.

You don’t have to use everything. Building boundaries are not building lines… and there are architectural subtleties that create a bit more freedom than the building envelope allows. The architect knows that.

Originally a basement was planned, then the whole thing could be somewhat spread out (office, pantry, utility room, technical room in the basement), but this was abandoned due to the high interest rates :(

I would probably reconsider all options with the small plot. A basement is actually possible with a smaller footprint. But also the garage roof is currently suitable for storage space and utility room... however, if the double garage is replanned into a single garage (for whatever reasons, I see the costs here!!!), then rather the house roof would be used to accommodate office and bedroom and thereby reduce the house somewhat, so there is a bit more garden and freer zoning on the ground floor. You have 12 meters of height available, which results in a nice attic where the roof is there anyway.

Who is responsible for the planning:
-Planner of a construction company

That's exactly how it looks :-(

I find the development plan excerpt interesting though. What are the maximum external dimensions for the house? Have they already been fully used in depth? Also for the garage?

The development plan excerpt is above all: too small (and too unexplained: does a boundary of the area of applicability running right through the property intersect a dashed line? - that would be a world sensation).

My impression is: they went to a general contractor here, and he - quite simply - "thought":
No basement >> fill the garage / carport special building window completely
Two parking spaces required >> draw two cars in the garage
No money to burn >> do not fully exploit the house building window
Three children >> mess around with some drawer draft accordingly.

Good-naturedly, as a diligent layman often is, one then hopes that one will only get a few small improvement tips in such a forum, because otherwise everything actually looks ready for approval appearance. FAR from it. Get yourself an independent architect (unfortunately you can put almost all general contractors in the same bag; with a simple three-child family they are already intellectually overwhelmed).

That's exactly how it looks :-(

I rather suspect that the template from the draftsman was botched by the OP himself. Just by the way, is the terrace allowed to be built in the clearance area to the street?

I estimate that the setback area on the street is not so problematic. I see many here who now also have their terrace almost directly on the street. And a new apartment building with 5 flats here in the residential area also stands 3m away from the street, even though it has 4 floors and is 12m high. I find that a bit strange, but the building authority apparently has some leeway when it comes to the public street (to what extent one can encroach on it regarding the setback area).

There is only one tree planned on the property in the development plan. I don't understand why exactly the driveway is being planned there. I would also be interested in the surroundings.