New single-family house approx. 190m² with double garage without basement - Design No. 3

We live here very rurally and the development plan is quite old (according to the building authority, a new plan would be too expensive). In a conversation at the building authority, I was informed that they cannot refuse me anything that was approved for others a year earlier. Of 20 houses, 8 houses have two full floors and a hipped roof or flat gable roof. With what justification should they not approve it for me?

You are building many sqm for few people. I would not position a study next to the playroom. The type of opening of the large living area to the terrace is an interesting detail. The line of sight can be stunning if the surroundings fit.

Of 20 houses, 8 houses have two full floors and hipped roofs or flat gable roofs.

How do you come to the conclusion that two-story buildings are not allowed?
Based on the floor area ratio and floor space index, two stories are very likely. You did not mention single-story buildings. Is something like that stated in the development plan? It is not always correct to assume single-story just because you read about a small KS. The development plan would contradict itself.
You also write: no slope, maximum height difference 90cm. That is a slope, admittedly not a big one, but it is a slope.

But whatever: so far you are only a little off with the DN.

Price estimate according to the architect/planner: 440,000 euros (house KFW 40+ including double garage

Personal total price limit: 580,000 euros including land (65,000 euros), landscaping, kitchen, furnishings

I find the construction cost estimate ambitious.

We are planning a quite similarly equipped single-family house to KFW 55 standard and have budgeted construction costs of 470,000 euros... I think that will already be quite tight for us.

I would be interested to hear what the experienced users have to say about the construction cost estimate.

How bad would a possible subsequent increase in construction costs be for you?

To gain planning security here, in my opinion you should definitely set a construction cost ceiling in the contract with the civil engineer/architect.

Regarding the floor plan: The purpose of erecting these light-absorbing mega partition walls to the terrace completely escapes me. You will always feel like you are in a tunnel. Get rid of them! Hedges or trees along the property boundary are much better suited for privacy protection.

I also find the shape of the open space questionable. A long, dreary corridor is difficult to furnish and hardly ever becomes cozy. The long glass wall can of course save a lot, as it visually extends the room outward. Nevertheless, I would probably arrange the bay window differently.

Upstairs, the children's area is in the dark north, while the bedroom, which is mostly used only at night, has the brightest and nicest location. That is upside down.

Music/Stereo wall
if possible Multiroom Audio

I can hardly imagine audio in the 4 x 11 room.

The long glass wall can of course save quite a bit, as it visually extends the room outward. Still, I would probably arrange the bay window differently.

I guess the panorama with the "tunnel" to the terrace was deliberately chosen because it was seen somewhere. However, one should check whether the room in the photo is not rather 6 meters or more in width.

Budget could be tight in BY, true.
Most Bavarians call for a price per square meter of 2200 for the Energy Saving Ordinance standard minimum requirement - without garage, without structural effort.