Do you want to keep the "black falcon oven" as the feature or do you want the island to be the feature? If you want to keep the oven as the "feature" in the kitchen, then I would do the island in the same cupboards and benches as the rest of the kitchen. If you wanted the island to be a complimentary "feature" to the oven, then you could perhaps do the same cupboards, but go with a black benchtop (although I would personally avoid a black benchtop due to it easily showing dust, water spots, etc). What material will be "under-bench" be on the island bench? Is it also going to be a feature (e.g. a graphic print, timber or something else)? Will the island bench have waterfall ends? If the island bench already has some level of visual interest, then it may not need anything more (i.e. different materials). You can always add visual interest to the island bench with accessories.

I'd pick the cupboard white first. Pick what you love. Then get the wall colour tinted to match the cupboards. Nothing worse than mismatched whites. Either match them or go a contrast on the wall.

i suggest 1200mm is the minimum along the length of the island and 90cm at the ends (providing the island is less than 90cm deep) but it really depends on the size of the island and the rest of the room

Your kitchen is a good size but not huge so I would go with gloss white to match in with your lovely fridge. All white appliances. Light coloured bench top in the grey range. Backsplash, I'd go to tile expo, choose something you love and add some colour behind the stove, the rest of the splashbacks behind the sink etc in white subway tiles. Dark floors as you have chosen, all the walls in the house Dulux Whisper White. This is a great colour to go with everything, i use it all the time in my designs.