2 offers for a single-family house in MV, large difference, is the offer plausible?

How often am I supposed to go to the professional? I will only go there with you when it comes to signing. Until then, thousands of things will still be changed. How do you now come to the assumption about Fiat and Audi? Don't you recognize qualitative differences in the two offers?

We are not a cheap cash cow.... see also my predecessor

What are the names of your two providers, feel free to send me a PM maybe I can give you a tip about local providers

We built in 2015/16 in MV maybe my experience can help.

we are not a cheap cash cow.... see also my predecessor

That wasn't meant like that.
In the initial post, I listed the points that caught my attention along with a few questions.
I wanted to hear your opinion.
Since surely some things are stated in the construction contract / construction specifications that I don't recognize, that's what the professional is for.

Thank you, Egon.

2. Energy certificate is not included; isn’t that a requirement of the Energy Saving Ordinance?

Basically yes, it must be handed over to you upon delivery of the finished new building.

5. Hairline cracks in the exterior and interior plaster can occur according to DIN.

Search for DIN 18550-2 online. There are interesting technical articles on the subject, unfortunately linking is not allowed here.

6. Untreated eaves box; that means I have to paint this myself, right?

Yes.

7. Rainwater drainage: no standpipes; so I have to install the rainwater pipe underground around the house to the central connection myself. Is that normal?

For most providers, yes.

The same applies outside. The provider said it can’t be done otherwise because otherwise the connection to the wall does not work properly and the insulation always absorbs moisture, for example if granite is used there.

Fairy tale time.

9. Room controller costs €40 net extra per room; isn’t that a requirement of the Energy Saving Ordinance?

Yes.

10. Is the wall construction with the insulation okay?

That depends.

11. 60 mm impact sound insulation on the upper floor; is that good? I mean, I don’t want to hear every little noise like in my last apartment.

That depends.

That doesn’t really help you, because with the new contract law / consumer construction contract everything is different anyway.