There are no hard and fast rules for tile orientation. You can run them whichever way looks best to you. My daughter and my son both recently redid their bathrooms and put 12x24 tiles stacked vertically on the walls. They didn't have to decide on vertical vs horizontal for the floor because they used 24x24 squares on the floor. In my bath I have 10x13 vertical on the walls and 18x18 on the diagonal on the floor. IMO the large square tiles make their small floor spaces look bigger. Do your tiles come in squares too? Maybe you could put them on the floor. If you stay with the 12x24s on the floor placing then horizontal ( long side parallel to the tub may make your room look wider). You can still put the wall tiles whichever way you want. Here's a couple shots of my DD's tiles Good luck in your remodel.

I’d suggest you use the quartz on you tub deck because tile sizes go in and out of style. Depending on when you sell, they can date your renovation. Regarding the marble, when I recently renovated my ensuite, I was strongly advised not to use it where water might sit because, in time, it will yellow, even if it’s been sealed. After I’d heard that, I realized that that was why my former shower threshold was stained.

@tartanmeup, the other thread was for vanity size and design. I was not sure if I can add tiling qs to that thread🙂. The bathroom update was a necessity as the cabinets are falling apart and vinyl tiles are peeling off. I was gonna replace the bathtub with standing shower too but she advised against it. So doing the minimum update to make it presentable.

The width of grout lines is determined by the edges of tile. Irregular shapes required wider grout lines due to variability of tiles next to each other. That’s why if you want thin grout lines you need tile with “rectified” edges. These allow for thinest grout lines. If they are “rectified” the tiler will have trouble laying without getting “lippage”. This is where one tile will be slightly higher than next tile. This causes tripping hazard so is to be avoided. Does your floor tile have “rectified” edges?