So it took a bit longer now, since during the drying phase of the screed the stairwell was closed and I haven't had the time to measure until now.
This is what it currently looks like, assuming a 10 cm floor buildup. I have not been able to get a concrete statement from my plumbing company so far. A bit sad, for the expansion I will choose another company...
The connections for the heating, toilet, shower, and bathtub have already been prepared. I have not drawn in the walls yet because I forgot to ask if the connection for the heating can still be offset through the floor buildup so that the box does not have to be placed directly there. But that should certainly be possible.
The knee wall is at 0.87 meters.
We will decide on a floor plan soon because we will completely cover the knee wall, the slope, and the ceiling with drywall so that the vapor barrier is not destroyed by UV light. Accordingly, we will have to plan the positions of the ceiling lights and sockets so that the corresponding cables are already pulled under the drywall to those points.