Running with your second floor plan (and ignore the glass sliding doors in this image) but would you consider changing your 3m narrow splash to a full sized fixed window on half the side and the remaining side create as the cooking area with cupboards, oven etc.? You mentioned you have stacker doors in the direction of the lounge, but in terms of space, from these doors, it's living area no windows at a room length of around 7m, followed by 4m kitchen room length including a 3m narrow glass splash to provide natural light for the kitchen area (cupboards noted above)? From your drawings there seems to be no windows on the opposite wall, is that right? I feel you will need to bring additional natural light into the kitchen area possibly bigger than the 3m glass panels if only 0.6m tall (or similar) especially with cupboards on top. If you're not keen on swapping out the narrow splash here's another example with your second floor plan (and also ignore glass sliding doors in this image) but possibly a tall window or fixed glass panel before your kitchen bench starts - even if <1m wide. Or greater than 1m if you're OK to encroach on your 3m glass splash and make it shorter. If the island bench is not a "must" you could create similar to this image and have a L-shape bench so it encloses the kitchen a bit more. This will help create the next room of your house ie. Kitchen - and you'll gain a few more cupboards if you're really wanting additional. Then have the big fixed window adjoining the L-shape next to the seating bench. You could still have your narrow glass splash with cupboards above, possibly just shorter (only referencing the L-shape and large door in this image - imagine fixed glass full-size wall panel in lieu of door next to the seats. Ignore the remainder of the kitchen). Is this an existing dwelling or new home build? For either of your options, are you impacting your roof-line as your first floor plan suggests you're widening the kitchen by 1m? The first plan I'm guessing will cost more; light wells and extra bricks vs straight wall. As mentioned by the other posts, there's plenty of storage options. You still have a decent amount of room for cupboards including a full-sized pantry next to your fridge space. I also agree with jbantick's of balancing space indoors and out (not knowing surroundings).

Southern light is usually more consistent and much softer. Northern light is good for warming rooms as the light is quite intense usually. Living spaces are good for Northern light but crap if you watch daytime TV as it can be too bright. Again all these theories should be based on location, shading from environment, etc. Our living areas face South/South West but is also elevated around the tree line. Many have presumed its North facing due to the amount of natural light we get.... the North facing area is well shaded by neighbouring trees..... My downstairs home office faces the South/South West and is perfect all year around, if it was North facing I'd have the blinds down as I couldn't see computer screen. Design to suit the site as well as the theories.....

It appears that the wall adds most of the strength to the stairs , so you'd want a builder that really knows what they are doing -- simply running a circular saw up the plumb line mark and removing everything above it may cause the steps to buckle or collapse -- steel beams would be unlikely back when it was built . An engineer may suggest removing the stairs altogether , and doing a new steel based one -- that way , you MAY be able to have say glass sides , or stainless railings , or similar , which will let more light in , but more $$$ , and possibly moving the apartment in a different direction decor and 'feel' wise too .

This is a good plan for the orientation. The north winter sun will warm up your living areas. Just have some kind of shade ready for the summer sun at the back of property. But otherwise a great plan. If possible you could open up the side northwest wall, but ensure you have coverage available for the summer western sun. The morning east sun will come into the home, so again for summer, maybe have some form of shading available when required. But for winter, will be perfect.