Full built ins across your window wall would look amazing. Maybe consider keeping drawers along bottom for a clean look and hidden storage for not so pretty items and then shelving above. Taking it all the way to the ceiling would look great too. For the short wall next to the door you could think about shelving to the inside of the window seating for a different look like the images below. We would love to see your final outcome!

luckily this shouldn't cause any major structural or safety issues and, even if it had been done "correctly" there would still have been some narrow cut tiles across the doorway so why not just add a row of tiles across the whole strip as a textural feature if you have matching tiles or a colourful feature in matching thickness different colour tiles or fill the gap with concrete stained or painted to tone with either the door or the floor or you could try a strip of wood but it may be difficult to cut a long narrow piece of wood thin and strong enough to survive the heavy traffic in a doorway although a piece of quad or scotia timber moulding or the curved edge cut off a piece of MDF skirting might be OK if sealed well...but hope everything else has worked out well for you

Hi Richard - the final kitchen layout looks amazing!! Congratulations. Any chance you could tell me what program you're using to design the kitchen / layout? I'm starting some minor renovation works on my house soon and would love to use something similar.

by "other options" i mean that you should consider all other options for locations of fixtures..there is already plumbing along each wall so swapping the location of shower and bath or vanity isn't as challenging as if there were no original plumbing in that area and if you plan to replace the fixtures and tiles rearranging the fixtures will only be a small percentage of the budget and it's a shame to limit the final result without at least considering other options..and although there is enough space to have the vanity hard up against the wall my suggestion is to have the vanity away from the wall to make it easier to clean and also because the small nook is an ideal space for hanging a hair dryer and with the luxury of so much space it will be easier to install a vanity away from the wall