Are you asking for recommendations in your area to replace them? Many such companies post on their local town FB for these jobs. I would take a look on there. I do have a company recommendation but they are Tamworth based in Staffordshire and don’t work too far out of the area? Are you close to that area?

A small word of caution. I think it could get very hot in summer in direct sunlight which would raise the temperature of your garden. I also wonder about durability. It is traditionally (as a material) not very strong. I would wonder about it's ability to withstand strong winds. I also don't really like the solidness of it. Quite sterile. Wooden closeboarding or slatted (vertical or horizontal) lets air through and weathers beautifully as do stone walls. I think it may turn into an aiirless hotbox assuming you are intending to use it for your boundaries. I doubt any breezes would pass though.

A back garden dwelling with kitchenette and toilet is classed as a separate dwelling and requires planning permission and will be subject to its own council tax payments. The planning application process will have stipulations about your neighbours right to the shared route as well as the impact on other surrounding properties. An initial conversation with your local planning dept would be a good starting point as you may find your plans affected by local precidents.

I think the pale colours draw attention to the fence more than it should. I prefer a darker fence that blends into the background. Or a natural weathered wood, which also blends into the background. Tbh I'm not loving the green woodwork, yellow brick and pink driveway combo. The render paint colour is also a bit too clean a colour and I'd rather it was slightly different to tone it down a bit and make it less crisp looking. I think the green fences look better than the pale neutrals, but I think I'd get the house exterior done first and worry about the fence later - at the moment it looks like you've not decided on the size/shape/colour of windows, in which case I'd reconsider the green.