Have a look at this thread. They used Cloe Tile with Silestone Eternal Calacatta Gold. It really looks gorgeous and I've bookmarked it myself for a future project. I agree that mixing the real marble with the Silestone may not work well. But I think you can put some sample boards together for your favourite choices and lean them up against the wall to help you visualize. You can also try different grout colours on your sample boards. The Cloe tile has significant variation and I think that is a plus. The problem of matching the white of your cabinets with the white in the Silestone and another white in your backsplash can be really tough. They are never all going to be the same and if you miss on one of the choices, then something is going to look dingy. But I think the colour variation in the Cloe tile will help with that, pull all the whites and some of the colour from the Silestone together. I'm sure it will be lovely. Please be sure to come back and post photos when you're done as well as work in progress photos.

Wait until the countertops are installed. Also, post a pic of the space :)

I love your soapstone!! For the floor, have you considered a wood-look floor tile? It would allow you to keep the same look even if you are changing materials. For the backsplash, I understand you wanting off white, but I dont think thats your best option here. Personally, I’d want to borrow light from the rest of the room and bring it into your space. You might have better luck choosing a very pale green with a light reflective gloss glaze. This is Spanish Merola tile that, interestingly, you can get at Home Depot. This is Heath Ceramics G11.2 Pisces Green

Just had a Viatera Clarino quartz countertop installed in our kitchen. We’re looking for some ideas for the backsplash. Thank you!