Hello,
on the west side, the property obviously needs to be secured. The house could overall be a bit taller if the wall height can also be measured on the west side. You can see this on the terrace in the illustration.
The adjustments to the prefabricated house would have to be discussed, Bien-Zenker also supports custom planning as far as I know. In terms of price, it is also cheaper than a basement.
Best regards