Thank you for the answers. Yes, admittedly we are having a bit of a hard time.
Unfortunately, your post didn't help much. Yes, we have been considering building for 2 years already. That’s why we have been keeping an eye out for a suitable plot for two years. We have realized that location is the most important criterion for us. The fact that we were offered the current plot is more or less a coincidence. I would also prefer if it were already a developed building area. Then, for sure, some things would be easier... From what you write, it seems no one should buy a plot or build a house if they haven’t read up on expert knowledge beforehand. But you might be right, and we are potential building victims. We have no idea and on top of that are very gullible.
I don’t really like that the size can still vary. I will call the municipality again on Monday about that. We have the development plan. We don’t yet know exactly what we want to build on it. As I already said, the location is the most important criterion for us. We don’t have a house in mind and are looking for a suitable plot; rather, we now have a plot and then have to find the right house for it. I could imagine that the issue of usability is mentioned also because groundwater plays a role throughout the whole town. In other words, if you even consider building a basement, it definitely can’t be done without a waterproof shell.
We will think about it further over the weekend and make some calls on Monday...