Hello Hugo,
for the first rough floor plan, I don't find the draft so wrong; there is certainly room for optimization here and there. Much of it is a matter of taste...
The direction of the stairs can also have a positive effect; we once had a similar living situation. The stair steps were often used as additional seating during parties in the living room. It feels open and friendly. However, with a lot of traffic going up and down and a greater need for quiet, it can quickly become annoying (especially when the children get older...)
I find the bathroom upstairs very successful; I would consider swapping the bathtub and the washbasins so that you have daylight at the sinks as well. Otherwise, it is reasonably well laid out for the size.
The bedroom seems somewhat oversized - but that's a matter of opinion.
I also find the arrangement of kitchen/dining room and somewhat separate living room successful; again, it's a matter of taste - some people love the open-plan all-in-one space, others dislike it. The same applies to the void space - with the size of your house, you can certainly do it, but you don’t have to. Disadvantages as mentioned by previous speakers.
What really is missing is some storage space and lots of room for wardrobes/shoes, etc. You have allocated too little space here; you should change that. The little bit under the stairs is, in my opinion, too tight. Think about how many jackets, handbags, sports bags, scarves, gloves, helmets, shoes, etc., accumulate with you - they all have to go somewhere.
With the hipped roof, be sure to choose the truss construction/roof pitch so that you still get 15-20 sqm of free floor space with standing height. It costs a bit extra, but it is worth its weight in gold. Accordingly, also choose a somewhat wider folding staircase - we thank our architect every day that we have this important storage space available. (We also have no basement, and space in the utility room is tight due to all the technology).
Don’t let the comments here intimidate you - a new floor plan proposal has never been received without a lot of (helpful) criticism.