Is terrain modeling allowed on the property?

Yes, my posts with external links were removed. I was not aware that these are strictly prohibited. Now I know, and I promise to improve.

When I have more information about the matter, I will get back to you.

The course of the road is close to the existing terrain up to about the road divider with the four parking spaces. At the bend of the road, it is already about three meters (and more) that the road runs below the existing terrain. From there, the most unfavorable part for the builders (on both sides) lies, with about four and a half meters height difference between the road and the building boundary at less than three meters across within the plots. That is unpleasant, but is at least compensated by a four-meter allowance on the eaves/ridge/gable heights compared to the neighbors in the "straighter" section. Apparently, a uniform slope of the road is intended here, and the junction into the Räriner Straße (District Road 6, which presumably cannot be altered under local municipal authority) is specified.

Quite clearly "yes," this section requires the most architectural savvy for skillful development.

And again quite clearly "yes": the steep driveways for the residents on both sides of this road section need to be questioned. Because for this section, the example drawing of the terrain modeling with the relative position of road/building is greatly misleading. So much so that the lay builder might not have been able to read this out in the disclosure.

You do need off-road vehicles (and later on rollators with power brakes) :-0

A small update:

After the last deadlines (suggestions, concerns, objections) for the amendment of the B-plan expired a few days ago, they were able to address my questions. Initially only by phone and therefore without going through the plans together, but they were able to somewhat "defuse" the matter.

A responsible civil engineer said that there had once been a plan involving a lot of earthworks (keyword "Canyon" for the street), but this has now been significantly mitigated by the amendment. There is still a height difference, but much smaller. About one to a maximum of two meters.
A friendly invitation to go through the plans together on site was also extended.

I think I will do that in the near future as well.