This is what I have in mind as a base:

Your architect and structural engineer should be planning this. No ripping down anything in a multi family building unless you yourself are a licensed contractor.

I think what you’ve proposed in your drawing is okay. You could also maybe put a bench in front of the window and then you’d have your own private waiting room. ;)

Ha it is starting to resemble a mini waiting room! I toyed with the idea of adding a little magazine basket or a small reading table but not sure if that's too much.

The previous owner is the one who built the house, and later divided it into apartments. He (large property developer in the area) had put in the false floor and told us it was stable and we could put furniture there - we felt it might not be strong enough, as it felt a bit weak when we walked on it. We pulled up a section of the floor to examine the structure, and the engineer who evaluated it told us we need further reinforcements, but it's just adding in additional beams between the existing ones, something a carpenter could help with. The engineer provided exact plans to give to the carpenter, of the size of supports needed, the necessary spacing between supports, and the method to attach them. To be clear there is a false ceiling in the entry hall for the building, then above the false ceiling, a plexiglass window that the balcony looked onto originally, and then on top of that, the false floor in our apartment. We won't at any time actually break through into the common entry hall.

We're doing a full renovation of the apartment, adding a mezzanine library in the double height living room and redoing the attic space (the attic is private to our apartment but we will need approval from the other owners for skylight/velux windows). For the attic it's similar to the false floor in the entry, we must add additional reinforcements in between existing floor supports per the engineers recommendation. We are also converting the long and narrow walk-in closet from the bedroom into the front hall closet, with one end of it becoming the stairwell for attic access - which is perfect because there is a nice tall window in that section that will brighten up the hallway now instead of being in the closet. We are working with a qualified architect on this, still only at planning stage. We are not making any changes to load-bearing walls and very minimal impact on party wall. The front entry area is the easiest fix, just reinforcing the floor and removing the balcony guard, so we're trying to move forward where we can easily make some progress.