So if it were my house, I would furnish the open space as shown. Two large beautiful plants to the right and left of the glass door visually separate the kitchen slightly, the fireplace is nicely visible from all positions, and from the sofa (which now feels much more protected and cozy) you can also look into the garden and not just at the wall. Where the chimney comes out of the roof wouldn’t interest me; the correct position inside would be much more important to me.
I would remove access to the utility room from the kitchen. Instead, put in 4 tall cabinets. Your kitchen is really big and for what still ends up in the utility room, you just take one more door.
I wouldn’t separate the cloakroom like that, better to close the stairs and build in the space under them. That gives significantly more space in the entrance area. Besides, it looks somewhat asymmetrical that way.
Regarding the sauna: 200 x 200 cm or 180 x 220 cm would be more practical because then 2 people can lie diagonally at the top. At 250 x 150 it will be difficult.
Alternatively, the kitchen could be like this: at the back, a cutout could be made in the tall cabinets. The window could be floor-to-ceiling.
