Organize construction electricity/construction water yourself?

Well, nevertheless, de GÜ occasionally demands that one be provided by the client

Sure, but we had clarified that another one may be used...

In our new development area, there are around 10 portable toilets

If you share in the costs, you are certainly allowed to use one... But probably nobody would care anyway, as not every builder even knows all the craftsmen working on their construction site...

And the screed drying with heat pumps mostly only works via the heating element.

I have learned from the geothermal probe company that screed drying is fundamentally not allowed to be carried out via the heat pump/probes (the probes could be damaged due to the high load), but only via the heating element.

Nonsense, it runs on both media. Especially at the current temperatures, the heating element is hardly necessary - only at high flow temperatures.

Always keep an eye on the brine temperatures, then it works.