A carpenter or joiner could make this. I’m a bit confused over why the title says out of Howdens units though. Am I guessing that you already have the doors from them? If not they’re available at lots of independent kitchen suppliers who I've no doubt will offer a more individual service than Howdens. Don’t forget Howdens promote the fact they only supply to the trade.

Your cupboards appear to be an off-white from the Yellow Hue Family. The further away from this neighbourhood you move, the greater the contrast in Hue, which will emphasise their perceived yellowness, as mentioned above. choosing a more colourful colour (more Chroma) from the same Hue Family, will make the cupboards appear more neutral by comparison. (Because they will be) Another alternative is to embrace the white, off-white scheme, by re-echoing it purposefully through the space for a subtle, sophisticated look.

It depends on what else you have in the room, the sofa colours etc. It looks to be a really nice room with some lovely features. Personally, I wouldn't paint it all a blue or a dark colour as East facing rooms can be gloomy on an afternoon. Have a look on instagram, there is a total shift away from dark interiors towards more neutral warmer ones. Not that this matters, but perhaps a year of lockdown has made a difference to what people want to live with.

There are ways of overcoming this issue if the right materials are available for your choice of manufacturer and the fitter has the requisite skills. I have attached a cad image of one solution. To answer your main query re: storage, the answer is as many deep pull-outs as you can manage and where the room shape allows, avoid corners! The main issue you have with this design is that it is unlikely to fit. If the corners of the room are not 90 degrees (which they never are) you will not necessarily have the 1840 dimension shown on the plan to fit in the tall units; without a tall filler beside the unit adjacent to the wall, there is no allowance for the walls to be out of plumb (upright), also there is no allowance for a corner post which is likely to lead to handles clashing. My suggestion would be to fit a narrow pull-out larder for maximum storage with a minimum 50 mm filler (preferably more). Increase both worktops to 650mm deep to allow for room discrepancies and the positioning of services behind units, with the added bonus of more worktop. If the hob is an induction model there shouldn't be a drawer underneath due to the cooling fan in the base of the hob, this could invalidate the warranty. We all want to fit in more than we can when planning our own rooms, it's human nature. A professional design might help to avoid costly errors at the point of installation and give you one design for multiple quotes instead of multiple quotes all with different designs.