I like the look of theTravertine paver colour 'Tuscany' as it will compliment both the house and the gambion wall. For plants, as suggested by Neryl Hollingsworth, camillias are evergreen and the flowers will add beautiful colour to the garden.

That timber top on the vanity would be tricky to makeover unless you had a piece of composite stone cut for it, or even a squared off laminate counter. It all depends how much freedom/budget you have. Can you see a time in the future that you are likely to update the bathroom completely? For now, it might be simplest to just paint the walls above the tiles Antique White USA and purchase a black bakelite toilet seat/lid. Replace the cabinet knobs with some shiny black round ones and the room will take on more of a classic 1920s feel as opposed to Victorian meets 1990 one.

I quite like the idea of using same tiles as you have around edge of pool. Here are some pics to help visualise how it might look. The last one has almost charcoal coloured tiles, which would look pretty good as contrast to your lighter tiles and the blue waterline mosaics.

I am no expert but I don't think they will work together. To me they are two different styles and if you use both it will look like a compromise of two clashing styles. I think you need to fully embrace the rustic or the vertical, use one of those as your feature and build around it. Question is; which one? Flip a coin?