Our island is 900 depth, 2400 wide, with a sink in the middle (opposite the cooktop), which works well for us. Plenty of prep area either side of the sink (mind you, it's a single undermount sink, about 500mm wide, with no drainboard). If we were going to use the island for actual meals, ours is only deep enough for a person either side of the sink. So, if you're thinking of having the island as a dining area, go to the 1200 depth. Just walk around it to clean it. On the other hand, if the island is going to be for prep, and a place for guests to prop up a glass of wine and chat while you're getting dinner, 900 is fine. Our dishwasher is to the immediate left of the sink, and we have pull out waste bins underneath the sink. We have 1200 mm space from island to the wall side and the range top, and about the same to the other ends. Our fridge, which isn't huge, is in a 900 mm+ cavity which would be big enough for a deeper fridge. It's in relatively the same place your fridge is, and works fine there. Hinges are on the non-kitchen side of the door, so it opens into the kitchen. Cabinets beside it are a bit more in depth, so fridge and cabinets line up nicely. 850 for your fridge seems reasonable to me. I wouldn't put that study where you have it: I think you'll need all of that butler's pantry for butlering type storage. My 5 cents worth based on new house, new experience, absolutely no kids in the equation!

It is a tough layout to work with - this might sound unusual & I'm not sure whether it would work 100%, but if you create a 'freestanding wall' with your bookshelf (or perhaps get a new one in white), with a low entertainment unit next to it, then shift the lounge against the long wall, you could possibly create a room rather than a space that probably feels like a corridor. Here's a very quick scribble to show you what I mean

Thanks Kate. Okay I can make that work w the pantry. So with that in mind, with the hinges on the correct side, you don’t think the fridge on the northern wall facing south will feel too cramped? It will come out 300mm more than if the pantry was there. But the win would be that the practicality and flow of the kitchen is there despite it coming out further.

something like this? and consider shallow wall hung storage across the whole long wall above and behind the AC and sofa and instead of the 1200 x 500 cabinet...shallow modular storage like those available from Ikea and similar could suit and they provide a variety of flexible sizes and shapes