I'm sorry to say that this comment won't be very helpful, I just wanted to say that that space is amazing! I feel like it has great bones and so much potential. It will look incredible when it's done. Oh, I did think of a tip but not sure if the stairs are too enclosed for it to work, but I love the look of white risers with dark wood/black treads.

depends on how often you need the extra bathroom and how much you prepared to spend? (i'd expect a modest redecoration of the old bathroom to cost about $15,000 without changing the location of any fixtures, a new kitchen about $15,000 and the second bathroom needing new complex plumbing, new walls and unexpected extras to cost at least two or three times as much if not more (assuming the BC agrees) and, where will you do your washing?.. contrary to other ideas i would prefer to keep a laundry without the second bathroom but removing part of the wall between kitchen and living area would allow for two options for a new laundry "cupboard" and a more spacious open plan kitchen, dining and living area at a fraction of the cost of the second bathroom...(say $40,000 for new kitchen, Euro laundry, floor coverings etc) my concern with the extra bathroom is finding a connection for the new toilet into the sewer which would probably involve digging a trench in the concrete floor to bury the pipe to connect the new toilet to the sewerage under the existing toilet ..my new kitchen and Euro laundry without relocating plumbing but, if you are prepared to completely rebuild the old bathroom and kitchen and rearrange walls this idea adds an extra bathroom in an easier location

Your apartment looks like it may have some Art Deco cornices, and with your beautiful gold drinks trolley and coffee table, I would use those pieces as your starting point. One large print/painting above lounge, with some gold in it, may look nice. Take the picture off the entry half wall, and place it on the slim wall opposite. Maybe in a new gold frame. I would put the gold drinks trolley on other other side of door, so it is a feature when entering home. With that wonderful bright art work above it. Is that a printer on the floor. If it is, it's probably a wifi printer, which can be placed anywhere in the apartment. Purchase a small Solid bookcase, to put this printer on. You could put your books and mail in this bookcase as well. Remove or items from the entry wall. Find a gold vase or sculpture for that wall, nothing else. You have to be strict with yourself in a small apartment. Do not leave things on dining table, or on the floor, find a home for them. Clear surfaces = clear mind. (Well, that's how I work, anyway)

is the room extra hot or cold as well as wet? start with asking the Council about building approval for the original sun room then a building inspection to identify the source of the leaks..there are Building Inspectors (check local services) who can give you a basic condition report for a fee..if the building was never a legal living room and has major problems with the structure it may be better to KDR but if the concrete floor and the roof structure are legal and in good fixable order then you might rethink all the windows, have the roof and guttering checked and repaired, lose some of the windows, reclad outside walls, insulate and line the inside walls to cover over the brick columns and make a more traditional looking lounge but, if you're not happy with the floor height, size shape or location of the room it may be time to consider a whole house rethink....to repair and redecorate the existing room and raise the floor (an extra slab or a timber framed higher floor to match the original house as long as the ceiling height will still be legal) but, without any major structural problems and very good luck with trades and materials) i'd start with at least $30,000 but to replace the whole building around $100,000 probably more but if you plan to spend that amount it might be time to rethink the whole house to make sure that you get the best value from a big renovation... there's a lot of different skills and tradespeople needed so the easiest (not cheapest) would be to employ a builder who takes control of the whole project, organises all the materials and different workers in the correct order and then you pay the builder for their services and they pay for everything but usually better to ask a builder for a fixed price contract so you know what to expect