Build a terraced end house with an additional unit (GÜ) on your own

Annoying, but that's how it is.

Not quite that simple. In general, only initial construction, subsequent construction/major renewal, and improvements are chargeable. The obligation to pay for a major renewal usually only exists if a certain period (usually 25 years) has passed since the original construction/last major renewal.
But given the impression the administration conveys here, they will probably try it anyway.

if a certain period of time (usually 25 years) has passed since the new creation/last fundamental renewal

I don’t see it taking that long here because the premature need will arise from not waiting, i.e., the completion while still being used as a construction road. Then the residents will object to the notices and they will be accused of not having prevented the nonsense "back then" (i.e., today) during the participatory process.

The picture is, however, very deceiving. Since the subcontractor of Netze BW has not yet closed the hole for the house connections, the screed sand could not be unloaded on our property. Otherwise, all other builders had to cover their street with appropriate protective foils to keep the street protected.

The street is therefore really still in its original state because everyone unloads their stuff somewhere on some property. That is also not a problem as long as no one else needs the space. The petty disputes like in other construction areas such as "but that’s my 5cm of property" don’t exist here. Everyone looks for the space they need - the rest is settled among the craftsmen themselves.

the screed sand

The bit of screed sand won't harm the pavement. The heavy-duty traffic will pulverize the pavement. Since the development carrier has planned that everyone is allowed to fill up their property by about 150 cm or build a basement, quite a few trucks will roll over it. One could ask the administration what the expected service life is under the specific conditions here.

It is simply common practice around here to finish the streets first and then proceed with construction. I see it all the time in the construction areas. If that were such a huge nonsense and the entire adjacent streets had to be redone immediately after the construction phase every time, surely someone would have thought of something. If the substructure is properly compacted, the streets will probably hold up.

We are still missing the top layer, which will only be applied once most of the houses are built.