Otherwise, I have learned that it is not a problem if the profile changes.
Learned… Where? Of course, if one wanted to, different staircases can basically be installed. Why do so few builders do it? Because there is a dependency between the stairwell, structural engineering, and ceiling. A staircase has to be supported by something; this works in a standard house construction through load-bearing walls. Transversely or vice versa, this depends not only on the load-bearing walls but also on the staircase. Or you focus on the staircase and then adjust the load-bearing walls accordingly.
Staircases with a central winding have either an additional load-bearing wall in the stairwell, a structural column, or a large open stairwell. But somewhere the upper floor must be supported and therefore the ceiling supported, and not just at the outer edges…. With a lot of money, one can plan very freely and elaborately, but that’s not possible with €550,000. That would be done rather in an open house over 280 sqm like at .
Then, of course, it is not possible to build over stairwells. One or two steps are okay. This steals headroom. Using a staircase with too small a stairwell does not work and no professional would plan or build it.
By the way, it’s also not visually appealing if you go from the ground floor to the upper floor and then have to look past a convoluted stairwell.
Be that as it may: I am rather irrational myself when it comes to great aesthetics. Spatial effect can create more size and airiness than 1-2 sqm more. However, one must probably bend somewhat or completely to their own family planning and give up one or more wishes if one wants to live a reasonably comfortable daily routine with 4 people under a DH roof over the years.
This includes room usage and necessary storage and shelf space.
Your staircase steals you several square meters from the living space without benefit. You extend the hallway through the staircase location into the living space, which is basically no longer usable except for placing a small dresser in the higher part of the staircase. The kitchen has a staircase hall feel; no one wants to play there, and daylight is hardly present in this area.
While a space-saving staircase integrates quite well in an RH/DH, this staircase location rather has disadvantages.
As already said above, the execution is rather questionable.
Regarding the design:
GF
Squeezing doors into a room corner is visually rather unpleasant for a room. Furthermore, there is generally no shelf space on the left side across the width. Any furniture there becomes a barrier. And yes, your cupboards probably _will not_ be enough for you four. A dresser or additional coat hook is hardly possible there.
Is the kitchen sufficient?
The hidden door to the freezer room also steals 2 tall cabinets… slim fridge and oven remain; then 2.40 m work surface. The island could be that long anyway.
The dining table is quite far away from kitchen activities. There is also a free area there that does not necessarily contribute to room design.
Living room is only suitable for a narrow TV cabinet.
UF
Children’s rooms should be oriented to the light and here to the south. The bedroom can share the side with the bathroom. Here too, the excessive length of the staircase backfires, so you can't place a door where it is needed.
The bathroom has unnecessary walking space in the entrance area and thus about 3 sqm less usable area.
Stairwell is built over.
AG
You have much space without fridge where you cannot stand. The bed will probably be very poorly usable. It’s best to plan the roof slope and standing area into the furnishing. You are left with a manageable room in the attic, maybe 4 x 4 m, and a narrow room as freezer/utility room plus storage/alcove. I see no hallway for space reasons. If you plan with a lot of window surfaces there, however, a friendly room can be created.
It is also quite different that one company has a problem with the statics on the GF for 8x12 m and another company doesn’t.
That may be due to different construction methods.
8/15 semi-detached house
You are restricted by a semi-detached house: here small plot and building window, no west side, entrance and staircase location is almost predetermined if you want to get the optimum out of it. I think it is wrong to want a gallery staircase and give away valuable space for it. At least for a staircase that, while in the middle, is excluded from the action despite kitchen proximity. It would be a foreign body in the house here.
I do believe, and have also seen projects where much more was made out of a MRH than the standard prescribes. But you don’t have to reinvent the RH/DH now to create airiness and/or generosity.
A nice classic but contemporary executed staircase, daylight on the upper floor, and no walls you run into—that’s already half the battle. The washing machine (HO) can go all the way up; then you can take care of laundry during breaks. Large gable windows up there would make it hard for the occupant to find their favorite reading spot.
If you cannot come to terms with a DH or its restrictions, then I would give the tip to keep looking and sell the plot again.
If you do, take some of the suggestions into your hands and try to make the design interesting with simple possibilities, which then also works.