I love what you've done so far - I would, however, change the light frame to a black one and add matting that is the same colour as the red in your hallway print that will tie your hall way and dining area together in a subtle way as well as making the print bigger - you could take the matt out by upto 15cm (more if you're brave) and the frame width of between 2cm up to 10 (again depending on how brave you are). As it's a rather large wall you can go bigger with the matt and frame as your wall can take it and you've been restrained with the rest of your colour and material pallet. Your plants are lovely but they're lost down on the floor in the corner - if you can boost them up (I've found pots turned upside down work and have also been known to use old pottery sewer pipes painted - they're totally clean of course!) so that they're a feature rather than an afterthought.

You could add a chaise lounge or a comfy chair and table for a reading nook or an office area if you need one, a computer area but whatever you do don't over clutter it keep it sleek and sexy and or a comfy chair as suggested with a little side table for reading, I also like the idea of a place to put coats, shoes etc if you must enclose it. Maybe even a small wine bar? with a couple of stools. I decided to google is and will give you a link to many pics to give you more choices. https://www.google.com.au/search?q=pics+of+what+to+do+with+space+behind+floating+stairs&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjFy-n9p4vZAhUEF5QKHSvhAOMQ7AkISg&biw=1280&bih=893

Depending on your budget and how much structural work you want to have done, you could keep most of it the same. But you would loose your meals room. extend your laundry to the door of the meals room, turn your laundry side ways this will give you access to the out side, on the other side of the laundry extend your wall pass the internal door of the meals room to create a walk in pantry, extend kitchen gallery to laundry and pantry, open up internal walls of kitchen to living room and dinning room creating a beautiful Island bench looking into living room. open up external dining room wall for sliding doors to bring the inside out. because there is a walk in pantry there would be no need for upper counters so u could also have a bar at the kitchen window on the outside. Doing it this way you would save a lot of money not having to move plumbing and electrical in the kitchen. You would have to walk through your kitchen to get to laundry though.

It’s the wall colour that doesn’t look nice everything else is fine. Repaint the wall it’s easy and you want regret it , use neutral colours but not light go for darker and for the corner I would plant giant bird of paradise either in the huge pot or if possible in the ground but keep it well away from the wall to give it space to grow and give you tropical look and feel. If you are using pots you can have few of them they won’t drop leaves in the pool.