I recognize in the drawing that your requirements are being implemented. If you look at the house only from this perspective, it can work – only with the costs I also have my question marks. The offers from the timber frame house manufacturers are unlikely to reflect the total costs; as a result, the design exceeds your budget by an estimated 50% additional costs.
Where could the necessary savings be made now?
In the living space, almost 30m3 are planned as a kind of dance floor. Now, one does not build the basement smaller than the upper floor, and there is reasonable saving potential of around 15m3 there. This saving is also easily possible in the cellar. So there is still space in the ground floor for a bit more hallway, and 15sqm over 3 floors less already means, with your (optimistic) estimate of €3000 per sqm, a calculatory €135,000 less in costs. A partial basement on the slope could save money again. Now, one can adjust something in the standard and the technology or contribute own work. With very high decision discipline, the €550,000 is within the realm of possibility.
With such striking area savings, a new design is needed.
Nevertheless, regarding the specific design:
1. Hallway impractical (already discussed)
2. Bathroom upstairs too small for what is supposed to go in. A T-solution works if the bathtub is removed. If there are children in their teenage years, the toilet will be used in the ground floor in the morning because the bathroom upstairs will often be occupied for a long time. Such a small bathroom in such a large house is – neutrally stated – unusual.
3. A storage room a bit more than 1m wide takes up a lot of space relative to its usefulness.
4. Why should a seating group be squeezed into a niche when a significantly larger area is available in front of it?
5. What is the purpose of enlarging the traffic routes with the strange door arrangement to the children’s rooms?
6. If there is already an island, then also with a proper work surface – or is that supposed to be a sink block? Again here: The kitchen is cramped and there is a huge empty space in front (apart from the dining table).
7. The dressing room is unusably narrow. If there is a wall full of wardrobes, you no longer have space to change or dress comfortably. This could be solved if the access went directly into the dressing room and from there a (sliding?) door led into the bedroom.
8. The basement looks as if someone thought – where to put all the space now – and just drew a few rooms.
9. If the slope goes to the southeast, I would, for light and cost reasons, also place the embankment in the garden there. That would mean a different arrangement of the basement rooms.
10. The way from the front door to the kitchen leads through the living room – past a dining table that looks like a barrier in front of the door, although the open space has so much room.
I often try to find the positive in designs. Here it is particularly difficult for me.