What is the difference in sound insulation between a solid house and a prefabricated house?

Does that mean that a prefabricated house built in drywall construction à la Bien-Zenker and a solid house "stone by stone" hardly differ in quality and living comfort (including soundproofing) in the end, if you get a good construction company with good craftsmen and a good site manager, [...]
Can it be summarized like that?

Yes, it can.

I am still open to both construction methods. I am currently trying to select some from the mass of possible providers (solid house construction, prefabricated house construction, architect),

There are more than two, and especially "solid" and "prefabricated" are not opposites: there are also some prefabricators who, for example, make brick walls completely transport-ready (and pre-dry them) in the hall. With such panels, the "construction time" is equally short whether they consist of wood or stone constructions.

Personal recommendations would obviously help enormously here.

In solid construction, in my opinion, the two most important recommendations are: "choose a contractor from the region" (which logically excludes a recommendation from Holstein being useful in Ingolstadt), and: "choose one who knows the building material." If you are committed to bricks, a contractor specialized in aerated concrete (or vice versa) is not the best choice. He will then do his usual routine without considering which details would need to be rethought. The same applies to monolithic vs. ETICS. Whatever preference you have there, the builder should share it. As you yourself say:

If a Schwörer house builds the design of Bien-Zenker or Bayerische Massivhaus the design of a freelance architect, it doesn’t feel quite right. It feels like the company architects always design what the company can build best themselves.

Solid builders are typically relatively small and regional, prefabricated builders active nationwide. Baumeister, for example, is a cooperation of solid builders. Or Hebel has an extensive range of kit types.

then ideally get a rough design for our house on our plot (we already have concrete ideas and example houses as templates for this)

You can already show the plot and examples here; impulses can be derived from that as to what and whom to recommend. Pictures can be posted here, external links cannot, but model names can be mentioned.

There are definitely providers who are better at slab-on-grade houses and others with well-coordinated basement builder cooperation. Depending on the slope situation, you are not entirely free concerning the basement question.

My feeling is that the person who creates the draft should ideally also build the whole thing. If a Schwörerhaus builds the draft from Bien-Zenker or Bayerische Massivhaus builds the draft of an independent architect, it doesn't feel quite right. It feels like the company architects always design what the company itself can build best. With anything else, you run the risk that the construction company says "Sure, we'll do it" but actually has to bend themselves a bit to get it done.

: Did you build with Schwörerhaus? If yes: when, where and are you satisfied?

Very uncomplicated and simple, everything is well-organized and complaints after acceptance were resolved within a maximum of 6 weeks. More emphasis should have been placed on the arrangement of the windows on the outside, but that was due to our floor plan; inside it fits well.

When it gets serious, I want to strongly emphasize 11ants' advice to think locally. Honestly, our construction is going very smoothly. The general contractor’s headquarters is just under 20 km away. He works only with craftsmen from the region, while the client is allowed to express wishes, which are fulfilled if they are reasonably priced, and he has a lot of expertise in civil engineering, structural engineering, roofing, carpentry, woodworking, and tiling within his own company. People know each other, they coordinate via WhatsApp. It’s working well, minor issues happen but no disasters.
Across the street, a regional contractor is also building massively. Groundwork started four weeks before us. Masonry began already in January, the house is similarly sized, but still no doors installed, no toilets, etc. Incredibly rusty old Sprinters arrived with wild characters, no company signs, trying to do work they really shouldn’t be doing. The construction looks cluttered, no one feels responsible, the site manager seems to want to remain incognito, the painting inside the house is partly acceptable, but in other parts catastrophic. The two older clients are just stressed out. And he’s not cheap either, only his subcontractors are the kind who every morning shanghai skilled workers in front of the station. Be warned. Local, nothing else. Karsten

You can already show the plot and the examples here, impulses can also be derived from them about what and whom to recommend more. You can upload pictures here, no external links, but model names can be mentioned.

Of course, very gladly! Attached is a picture of the plot.

On the neighboring plot to the left behind the hedge there is now a new single-family house up to whose building line we may build according to §34, so about the first two-thirds are buildable. To the right is a field. Everything is very flat. In total it is 1,018 sqm. We are planning a 2-story single-family house (ground floor and upper floor) with a total living space of 250 - 300 sqm plus double garage, terrace, and pool.
Also attached are some house examples that we really like. Most of them are from Bien-Zenker, we really like almost all the houses here. Our favorite here is the Concept-M 211.


Thanks again to you for the many great tips

We had also once flirted with the seventh house of the facilities. But finding a room layout that suits us would have been difficult.

The symbiosis terrace / pool at the sixth house is really great! It really makes you want to!

Sure, with pleasure! Attached is a picture of the property.

Based on the aerial photo, I estimate that it is quite level as well? Is that what is meant by the development (and all existing buildings that will be removed)?

We had also once fancied the seventh house of the developments.

With this Heinz von Heiden Arcus WD you can clearly see which roof overhangs and parapet thicknesses I consider aesthetically appropriate: at the top for the hip roof slightly more than remains in front of the bay window, and below you see a good overhang and a good parapet thickness for a flat roof, where the balcony protrudes. In all dimensions about half, compared to your then spaceship lid roof.