My ideas about the floor plan come from...

It has to work, the design.

It does: Ikea shelves can be passed through the airspace of the stairwell.

I can tell you from experience: The hallway is too small! I had such a thing in my first own apartment. 2 adults couldn’t properly get ready side by side. A coat rack fit, yes. But it took up a lot of space, especially in winter because of the coats. My almost mother-in-law was a bit stocky and had quite a hard time maneuvering in the hallway. She then always undressed in the adjoining dining area and draped the jackets over the chairs. Why don’t you remove the walls in the intermediate hallway and thus enlarge the hallway. You can put the walls back later if you want to separate the upper floor again (why actually? Is it supposed to be a granny flat? Are the connections for the kitchen already planned there too?) I also find the kitchen a bit narrow for a U-shaped kitchen. As soon as a drawer is open, it could get tricky. The bathroom is then also a clever trick with a slope. Where is the shower supposed to be installed there?

The bathroom is then a clever trick with a slope. Where should the shower be installed there?

Oh yes, hehe. I completely overlooked the gable roof and the eaves height - since this design on the upper floor can only work with a flat roof or at least knee wall of shoulder height, I had naturally assumed that. Hmm, yes then it might actually be difficult to hand over a shelf unit after all ;-)