Hello, first of all I have to praise you for having used your time and put a lot of thought into this.
There are many good detailed considerations that you want to implement.
But the house actually looks somewhat uncharming, even though I really like 60s/70s architectural styles: somehow it lacks the sparkle that was used in the past.
Are the windows placed somewhat arbitrarily? I would reconsider some of them for the sake of the façade.
Also, I notice that a lot of love was put into the parents' rooms, but the children get a bit shortchanged. On the one hand, they are relocated to the north, on the other hand, I can rather imagine that children would benefit more from a window seat as well as a bathtub than the parents.
Since you asked about roof usage, I would basically suggest thinking about an offset shed roof with rooms open to the top.
Lower the roof structure further down on the south side, use the third gable to indirectly illuminate the children's rooms with higher placed south-facing windows.
However, then, for example, some of the windows on the south side on the upper floor would partially disappear. But that would fix my second criticism, namely: even if there is nothing out there in the middle of nowhere, it would, in my opinion, not be comfortable to have such open windows in the intimate areas showing you completely. I would probably rather use a skylight in the dressing room as well as in the bathroom, which ensures brightness but also privacy. There is the east window in the bedroom anyway. South windows in the bedroom would probably always be closed due to the heat; in the dressing room, the clothes would fade...
I personally find the bathroom too big and thus uncomfortable, but that is up to everyone to decide how they want it. For the sauna, I would probably want an outside access as well.
Then, of course, there are many empty spaces. Large rooms in the basement do not mean that furnishing becomes easier, especially with storage rooms and utility rooms where you need more walls than space.
I would divide the background kitchen: separate storage room - shelves on the left/right, two doors.
I would recess the guest bathroom and place both elements side by side... although... somehow the hallway doesn't flow... I don't like the idea of the three separate closets at all...
I think the kitchen with a scullery is great!
Edit: why not close off the gray area of the scullery as a wardrobe?
Since the basement is still for storage, a good hidden meter is enough for the kitchen, that is, what is currently shown as “colored.” Access from the kitchen is also sufficient.