Floor plan design new single-family house 2-storey approx. 135 sqm

I think the plot was two posts earlier. Here again as a reminder:

Now I would have actually expected a sketch ;)
… and the answers to my questions ;)

I have already met with a few providers, Hanse Haus, Gussek Haus, Bien-Zenker, Schwörerhaus all appealed to me and seemed competent if I can judge that. Should I engage more intensively in a conversation with one or two without a floor plan and have them make proposals?

Several things irritate me about these sentences: what does “met together” mean? Did you talk and chat concretely with a (trained) salesperson in a display home? Specifically?

Or rather go directly to the architect, although it is probably not easy to find the right one there...

Have you actually tried that?

Or is a prefab house consultant (salesperson) able to keep an eye on the legal matters? I assume the salespeople are not architects...

I have the feeling that you have not even approached professionals at all with your wishes, questions, and your specific plot and house construction.
I mean: there are steps to take towards possible building partners that you yourself have to take – if necessary, multiple times.

We have now also chosen a house from the brochure that corresponds to our ideas and where not much needs to be changed.

Why shouldn’t something be changed there?
The urgency to commit irritates me, especially after being actually satisfied with a house of a completely different style just a few days earlier.

Now we have to see if other companies can manage it similarly. So we mostly stay with the standard and as soon as it goes on or the new floor plan by the professional is finished, we will see...

For the other companies, it is not a standard but an individual unique solution, because only Massa Haus builds Massa Haus.

In post #42 I agree with : it makes no sense at all yet to ask “any companies” for an offer.
Every company has their reference projects that you can gladly inquire about and then compare with the building service description in hand or on the desk plus Excel sheet. One may come in €20,000 more expensive for the house, but you have free choice for window areas and twice as many electrical installations and better insulation included.
Especially home builders each have their company philosophy; the building partner must also fit emotionally. Not only the number at the bottom right, which companies roughly estimate without signature merely by square meters and construction type, is important, but precisely the building service description.

I suspect it will still take a while until signing, but I believe we are now on the right path.

to commission a soil survey and a surveyor

This path is definitely the right one, but you should speak more concretely with the individual companies. Then you get a lot of input…
and not with the first five who pay the most for their ads on Google and then you with them.

Guys like you really ruin this place, so many people try hard here to help beginners and to have a friendly interaction with each other, but you keep blowing it.

At least he responds. And has spoken much truth, with which others agree by liking.
There are MANY active people here who could say something but don’t. Where chopping happens, chips will fall.
You can also just overlook bad days.
In that respect, if I were you, I would either overlook or ignore “bad posts” or simply apply the tips from them or think about them.