I really like the floor plan. Although a lot of space is massively wasted due to the entrance area with the "double" corridor on the ground floor and the open space on the upper floor, the effect will definitely be very cool.
Oh yes, 500k for the place with a basement, never; 600k including fittings will very likely not be enough either.
Where do you want to build?
Building in Hagen (NRW), yes, my wife also only wanted to spend 600,000 including the plot, now we have planned 600,000 without the plot, let’s see what it ends up being. But at 43 I’m not going to build again, so "what’s the point of being stingy" it should be GOOD!
I will build smart and I still have 50,000 in my secret compartment.
We saw something similar in the floor plan in Wuppertal in a prefabricated house park and it was the only thing we liked immediately, yes a lot of space wasted but you can install an elevator in case something happens or so.
Regards