Am pretty sure that if I was a kitchen designer I wouldn't spend hours working out the cost of a kitchen that likely won't fit. However I have met several who could tell you if the budget you have in mind is enough to fill the space and perhaps direct you to some of the cabinet and worktop choices in your budget so that you can start to get excited about eventually planning your kitchen. It might even be possible for the company you choose to visit the house to measure with the current owners permission. What area are you in? Perhaps people could offer recommendations for kitchen studios?

If you are going for a natural stone /granite etc type top - that might limit you, if you don’t want a seem, as they are only available in certain sizes . Also its wise to go for a size that you can easily wipe without over stretching yourself ! Think about how you will get it into the room too -as they can be pretty heavy !

I think 1200 is a good clearance- I have 1000 which is fine but they reckon that 1200 is right if you have two people in the space. If you had a smaller island I think the island would look too small so I wouldn’t make the walkways bigger. In addition you currently have a foot hole for the stools that is 2200mm- in my opinion this is more comfortable for 3 stools than four so you certainly don’t want to go smaller. In fact you may want to swap the 300mm units and replace them with end panels. I hope you don’t mind other observations too. To continue the symmetry I think I would centre the range to the wall and island. Perhaps 900mm drawer units each side of the range would fill the space and personally I would rather have drawers there than behind you when cooking. I think I would also swap the extractor hood for something more decorative since it is the only thing you see when sat at the island. For me I also feel that the American Style fridge has had its day in high end projects and I would rather see two integrated appliances. You could have a side by side larder fridge and larder freezer that would have more chiller space than an American Style fridge or you could have 70/30 fridges side by side. You can get a 900(ish) wide integrated fridge freezer too but this is often a more expensive option. For visual interest interest you could fit this wall with a breakfront. Personally I think the island is one place you don’t need symmetry. Personally I would put the prep sink at one end so the prep area is uninterrupted. I would also include a large pull out bin cupboard so you can easily dispose of recycling and food waste. The island also seems like a great place to integrate a microwave rather than having it cluttering a worktop. Lastly I think I would probably add either some wall cabinets or paint the sink wall in the cabinet colour to balance the tall units at the other side of the room.

As he supplied and fitted the kitchen, then he really doesn't have an excuse for not knowing the sizes of the cupboards to which you were referring and wanted replacing. However, if he wasn't sure he should have double checked with you. Plus he should have ensured the drawers he was making up, were the right size before constructing them. Personally, I think it's all down to him.