Can you share pictures and/or links for your materials? It is sometimes difficult to envision material combinations when you can't actually see the materials. However, imagining the tiles from your description, I think the combination of slate and white would be lovely. Will the accent at the top of the shower be of the same granite as the vanity countertop? If so, I think either using the same granite for backsplash or the pearl white glass accent tiles as a backsplash would be lovely (or even a combination of the two). I suspect any color of wood would go well with your selections.

"brown fiber like board" , this sounds like nothing waterproof or anything that belongs in bathroom in my opinion and looks doesn't mean it is correct. I agree with your second contractor if one is crap the odds are the one that looks good is s well.

Has anyone ever used this tile in their home. I'm using it for a bathroom floor and wondered if a white matte subway tile would match the floor. The subway tiles will also continue around the tub as well. Any suggestions would be greatly appreciated.

Small bathroom with no windows. Very little cash to put into it