Your green house is 10m*13m, the garage 6m*7m, the driveway 6m*11m. The house therefore has a footprint of 130m². As a single-story house, that would result in about 104m² of living space, as a two-story house 208m², both far from your target of 150m². With a building window width of 17m, 11m remain for the house after subtracting the garage. Maximum footprint thus 11m*15m=165m² equals about 132m² living space for a bungalow. Or conversely: 150m² target living space corresponds to about 190m² floor area, distributed over two floors results in 95m² footprint. These are optimal conditions for a so-called city villa (10m*10m, two-story, hip roof with 20° pitch). The floor area ratio should not cause any problems. For the bungalow, it results in Floor Area Ratio-1=132m²/555m²=0.23 Floor Area Ratio-2=132m²+42m²+66m²=0.43, permissible if §19 (4) BauNVO is not excluded by the development plan. For the city villa it becomes even more favorable. Regarding the hillside location, I see no particular difficulties, as the height difference within the building area is only 1m. I do not see the basement as essential there (although I would make one), since the plot is large enough for terrain adjustments.