Which construction company? Based on what criteria to decide?

Got an offer
25 pages where all trades are listed in great detail and what they cost.

Still, does the 5-person company have an additional construction description like the big providers?

Great that you use an iPhone. That’s completely irrelevant here and can be turned off.

Whether your 5-person company has a construction description, you have to ask them yourself; we can’t tell you that.
A construction service description is not meant to define the final equipment but to specify the service behind each trade.
Example: Provider A does the exterior walls this way, Provider B that way. In the end, they achieve the same insulation values.
And if the construction service description only covers a cheap exterior plaster, you can still choose a better plaster...

Whether the craftsmen leave their construction site clean, I would not consider a decisive factor. The work counts.

What matters:
-quality
-good impression
-you need to have a good feeling about the final sum
->price/performance

= good feeling about the contracting partner

I also don’t see experiences from other builders as an objective indicator: you first have to look at what kind of person the builder is. There are impossible builders who rate impossibly and speak badly. The company can be as good as it gets.

Testing everything out is usually not possible. Five builders can praise the speed and adherence to all dates, but at the 6th build there may be a frost period, a water damage, or a wrong delivery so the final date can’t be met. That doesn’t make the company bad.

Whether the craftsmen leave their construction site clean,

... is in my experience a good indicator. Structured processes and internalized customer orientation, including the hand-in-hand thinking with neighboring trades, almost inevitably also produce a tidier construction site as a side effect. Like master, like crew. Those who are sloppy also don't see how much mess they've made.

One more question.

A construction and service agreement would be good if it existed. Is this standard also with smaller companies?

Yes.

Mandatory since the beginning of the year