May I suggest contacting the interior designer to request information on the tiles?

Have you already sourced your tiles? I would expect most tile stores could help you find the edging tiles which I think are typically termed 'pencil' tiles for the style you have shown. We used bevelled subway tiles in our DIY ensuite. In hindsight we would have aimed to finish the brick pattern with 1/3 and 2/3 sized tiles (like in your pic 1) rather than full and 1/2 (pic2 and 3) to give a more even edge thickness/profile... Might not suit and we didn't use capping tile (I lost that arguement!) so it is probably more obvious in our bathroom, but just something you might like to consider.

I would have thought the intent of mosaic feature was to highlight a feature by drawing your attention to it. I assume the bath and window is intended to be a feature, so why not tile above bath & around window to draw attention to that.

This isn't a personal recommendation as I have not yet purchased anything from this company, but I've been admiring the timber floating shelves on their website. https://shelvingshop.com.au/product-category/floating-shelves/wood-effect-finish/ Or you can buy the brackets and have the shelf custom made in whatever material and size you want. https://shelvingshop.com.au/product-category/brackets-2/floating-shelving-brackets/  I think hardware stores also sell brackets by themselves. I was thinking of going the custom route because that means I can ensure the brackets will be attached to the studs. I believe you can paint melamine after proper preparation of the surface, but I doubt if you can stain it.