hm… I think point 2.4 explains quite well how high your EG is allowed to be. If you build without UG, then OK finished floor EG applies. You just need to use a set square for that. Removing or filling in is usually not desired in these building areas, by the way. That is why the builder is given the option with the possibility of building with UG. In my eyes, a fair compromise.
If you only want to build 80 sqm, then that is your individual fate and actually does not fit at all in this building area.
I myself have little contact with slopes and personally don't like cellars either. But in a neighboring town of ours, there is an extreme incline on a residential street. There you see the beautiful terraced houses clinging to the slope, mostly with generous window areas on several levels, each individual house an architectural unique piece. Noticeable are here and there some with a rather steep staircase leading serpentinely to the front door. However, the foundations at the front of the houses without UG are no longer visible, as they have been integrated into the garden design over decades. When you write that you only want to build 80 sqm, I ask myself whether you have already factored in the technology and storage space, which is otherwise the cellar room in an apartment. I’ll put it this way: it hardly makes sense to build a 2-room apartment as a single-family house. Even less so on a sloping plot. Not economically or financially comprehensible. Since we do not know your space program here, I’ll take the offensive and ask whether there really is a realistic space program for you or a bungalow. If you still see potential there (you can also have your ideas for a house design discussed here), then I would consider a hobby room or another nice feature of self-realization, which could have room next to the freezer and storage room in the UG. Because you have to use stairs anyway… the plot is definitely not barrier-free and will not become so. Otherwise, I would advise you not to buy this plot in your place.