Construction of 2 retaining walls, development plan BW

no, but I want a plot of land that is flat.

And I want a large mixed ice cream with whipped cream every morning, preferably on a doctor's prescription!

And whether I plant rice there or build myself a railway on which I can drive around my house doesn’t matter.

Whether everyone violates the topography of their landscape is not indifferent, but egotistical and "geographically antisocial." You talk about one and a half meters of slope (across the entire property! – others already have more under their houses alone), this can be calculated and gently shaped. With any floor area ratio significantly below 1.0, it is also meant that you cannot play marbles or set up a coffee table without leveling wedges in every little corner of your property. A rotisserie grill won’t tip over there yet.

And I want a large mixed ice cream with whipped cream every morning, strictly on a medical prescription!

Whether everyone violates the topography of their landscape is not indifferent, but egotistical and "geographically antisocial". You talk about one and a half meters of slope (on the entire property! – others already have more just under their house), that can be calculated and gently modeled. With any floor area ratio well below 1.0, it also means not being able to play marbles in every little corner of one’s property or place a coffee table without wedges. A swivel grill won’t topple over there yet.

It’s already a cost saving that the earth that is excavated does not have to be hauled away but only distributed. And that is also environmentally friendly :-)

.. you seem to be underestimating the costs of a retaining wall.

There is already a cost saving since the earth that is excavated does not have to be transported away but only redistributed.
And that is also environmentally friendly.

Yes, that would indeed be more environmentally friendly if you did it that way. However, you still have to add a little fill when leveling out, because the spoil loses volume after compaction when it is rebuilt.

.. you seem to be underestimating the costs of a retaining wall.

The square meter of retaining wall with foundation is 180€.

Yes, that would indeed be more environmentally friendly if you did it that way. However, even when filling, you still have to add a bit because the excavated material loses volume after compaction during reinstallation.

If I roughly calculate it, it should almost fit.