Thanks for the comments, we will take them to heart and discuss them with an architect. Children’s room a bit bigger, utility room a little larger. We'll find a solution for that.
The west balcony can also be accessed from the office. We don’t find that so bad.
Stairs accessible only through the living room also have their advantages. You know who goes in and out and when. :P We also saw it more as a visual highlight.
We’re putting in an air-to-water heat pump, does the technology really need so much space that it could get tight for the washing machine/dryer?
The fireplace is planned as a decorative element (ethanol or similar) and therefore no chimney is required.
6m ceiling height is of course total. We plan downstairs 2.6-2.8m ceiling height, then the ceiling, and upstairs up to the slope 2.6m, to the ridge 4.0-4.5m. It’s still open whether there will be an attic after all. Visually, we have seen several open ones (of course partly with open and partly lowered ceilings, for example in the bathroom) and we liked them quite a bit.