I think you need to get a decent independant kitchen designer involved before any works is started to work with you and your wishlist and work from the architects plan. Your local sheds and builders merchants are very limited in what they can offer, (might be lots of colours and fancy bits etc but limited in door and cabinet size options).

Looking quickly through your listing and i'd say

appliances, you need to start looking at these so your designer can fit them in your kitchen, add what you need to your wish list, but a 600 wide hob may well be to small if you like cooking, possibly move to island and have a downdraught extractor ducted out before any concrete/floor goes down

you can't have to many drawers but drawers do start to bump the price up

extra tall units to go close to the ceiling then have a head infill (about 50-100mm) to fill the gap and then it won't collect dust

in the corner, i think if this is in the extension, then the window may be to close to the corner, would need to see measurements. possibly would run wall units here

would need more wall space to fit a breakfast pantry unit in the kitchen (plenty of space eleswhere though)

You have a really lovely large space. I agree with Lifestyle Kitchens that your design would benefit from an independent designer, or at least thought through by another supplier to spur ideas. From my perspective....

Flow: Consider the spacing between your sink and hob... I think yours will feel quite cramped when in use. (Imagine a spoon rest, chopping board/ prep area, dirty dishes, etc). If you want to keep both on the outer wall, and think you’ll prep on the island, I would consider putting in a small prep sink. That will also help you interact with any kitchen guests, instead of always having your back turned to them.

Where do you plan to keep your dry goods? It appears all your pantry space is in the adjacent room. Perhaps one of the 3 oven towers could be be repurposed?

Appliances: The 60cm hob does seem small/imbalanced for the overall space. You might not “need” anything bigger, but a slightly larger hob will be more comfortable for any multi-pot meals.

The Clock space.... 2 floating shelves for cookbooks and/or display items and plants would look nice.

Drawers: The design does seem to be missing obvious shallow drawer space for your cutlery, knives, cooking utensils, foil & clingfilm etc.

Concept designers.... We used Karen at https://www.oneplan-design.co.uk/ early on in our kitchen remodel design thinking. It was money really well spent, and I learned so much.

Concept

Thankyou! Really helpful. Will take a look at one plan! 👍

I have a pro page on Houzz too - click on my name or icon to get there ! Thanks for the mention PJDKLM !