Thank you for your help. Here are the after pictures excluding decorative accents. Wall paint BM Palladian Blue, floor tile 12"x3" grey marble polished porcelain, accent wall tile 24"x12" white marble polished porcelain with white marble stone pencil border.

Here is an option if you prefer the checkerboard design using 2 different tiles. I think they would work nicely. The Ebony Marble design is forgiving in colors used, not too black and solid. The white in it might be a soft white, not too white. Maybe samples would help. The size tiles and dimension thickness would have to be the same. I did not verify these. Ebony Marble https://www.lowes.com/pd/Style-Selections-1-piece-12-in-x-12-in-Ebony-Marble-Peel-and-Stick-Vinyl-Tile/999978538 The Crescendo might lean to an off-white. Crescendo https://www.lowes.com/pd/Armstrong-Flooring-Crescendo-12-in-x-12-in-Groutable-Marble-Look-Peel-and-Stick-Stone-Look-Commercial-Residential-Vinyl-Tile/1001435690

Yes. Draw out a cube (or separate walls) of that size. Then try placing 12 x24 squares on that wall. You are going to have one whole tile in the center of each short end and 6” wide pieces on either side, or a 1 ft piece on one end. Do you like that look? You will have 2 and a half tiles on the long side. If you switch the orientation of the tile and put the narrow side down, you will either need to have the walls widened by the space of two grout lines, or have one side of one tile cut just a tiny (likely jagged) bit. Make sure your tiler can cut those edges well, because, the tiles being so big, the jagged edges become very obvious. When you have a busier wall of smaller tiles, they do not stick out so much. Only if you make the shower exactly the size of the tiles, plus the grout, and lay them in a vertical stack, will you get rid of cut edges. Play with layouts and see what you like. You can also consider Corian or Swanstone and have a life-long beautiful shower wall with no grout. Anywhere. If you vacuum or sweep regularly, a black floor can be nice. That is, unless you ever use powder. If you do not clean your floors regularly now, do not think about a solid dark color for the floor. Floors are not wet all the time, so their grout should not discolor. You can have more grout lines on a room floor than in the shower, without mold or mildew.

Looks like the OP has that wall tile around the shower threshold and, I assume, the walls too, so not that easy to get rid of the wall tile. Maybe just reducing the amount of the wall tile, except for shower area, will help tone down the discord between tiles.