What does the property look like? Please draw 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 doesn’t make it bigger. On the contrary – the staircase immediately 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 more whether it deserves its name given the size of the house. What you have drawn there is not a gallery, but rather a peephole. I think it’s nonsense to accept the disadvantage of no longer being able to reach the windows on the upper floor for that. Besides, it looks lousy, if you ask me. The gallery needs space in order to have an effect. I still see possibilities on the ground floor, but it will be tight on the upper floor. With 3 bedrooms, a bathroom, and a dressing room, there is hardly anything left at 140m². If one knew more about the property, one could still puzzle a bit.