I would definitely change it as well. Also because of the storage space, which could then be used much more effectively. But cleanliness is also relative... What is clean for one person is a pigsty for another...
I would change it too, especially since it eases the entrance situation on the ground floor a bit. However, you will then have to check what happens with the window planned there in the stairwell area. Possibly omit it.
... what will happen with the window that is planned there in the stairwell area. Maybe leave it out.
Yes, can you even just leave it out with a prefab house? If yes, will it still look good then? It will of course be darker. I also think it's a shame about the gallery. For example, you can hang laundry there in winter if necessary or set up a small play corner. Well then, you have something to puzzle over.