What does the property look like? Please mark the cardinal directions on the floor plans.
I consider a ceiling height of 2.75m to be exaggerated for 140m². It is a rather small house. Raising the ceiling disproportionately does not make it bigger. On the contrary – the staircase requires much more space if it has to cover more height. A good size in my opinion would be a clear room height of 2.55m to 2.60m. Accordingly, the staircase would be about 2.90m high.
I don't think a gallery in the entrance area is impossible. The question is rather whether it deserves its name for the size of the house. What you have drawn there is not a gallery but rather a peephole. To accept the disadvantage of no longer being able to reach the windows on the upper floor for that, I consider nonsense. Besides, it looks awful, if you ask me.
The gallery needs space to have an effect. I still see possibilities on the ground floor, but it gets tight on the upper floor. With 3 bedrooms, a bathroom, and a dressing room, not much is left at 140m².
If one knew more about the property, one could still puzzle a bit.
Here is the site plan. I cannot mirror the floor plan. If I orient the bathroom facing north and the bedroom facing southwest, the bedroom will be directly on the street. The same applies to the living room. Every time people come to the front door, they can look into the living room. I don’t want that. The sofa can be rearranged; it’s not permanently fixed. More windows will be difficult. To the west of the living room wall, the garage is planned. What is wrong with the width of the toilet area?With all due leniency: you were asked for a site plan. The plot must be very "interestingly" located for the bathroom to be placed in the southwest and for a child to only get a north-facing window.
Sleep on your floor plan for one night and then think again, for example, about the width of the toilet area on the upper floor or the expected feeling of sitting on the couch in the middle of the room with your back to the door. Or, in general, how pleasant it will be in a living room with only north-facing windows.
Edit: to the admin: I do not find it acceptable that links are inserted in my text – presumably advertising?! – These links are a reason for me to consider unregistering from here!