Hello Maju & Co,
I registered here especially because of you, as I find your pragmatic, open, and fearless approach very likeable.
Independent of room layout and other already mentioned points, one or two food for thought from me:
As I understand it, the basement is almost completely buried and only the small office has living quality. If you can do without that in the basement, the basement could possibly be designed purely as a utility area. So without insulation, sealing, waterproof concrete, etc. Just raw concrete to house cars, bikes, garden stuff, and building technology. The entrance would probably then have to be taken out of the thermal envelope and possibly protected from the weather in another way. I am not an expert, but maybe that is simpler, more fault-tolerant, and cheaper. Even if you take the saved money for enlarging the ground/top floor, I would still find it better because then you gain "above ground" living space and reduce stairways. In this context: why is the house actually narrower at the back? That only results in shadows/dirty corners, especially since the view goes forward, right? If anything, I would make it wider at the back.
Otherwise, I am looking forward to your next posts with excitement. It will definitely be great!!!