I would do a glass splash back [ this can be painted in your color choice to suit the decor ] - taking from the bench top up to the bottom of the range-hood on the wall of the stove. The window is beautiful and I would give anything to have them in my kitchen. I would probably paint OR stain and apply marine grade vanish to the would so that any moisture would not be able to ruin the wood. I would also put herbs or flowers there. Could it be made into a servery for outside maybe ???

I would not try someone who's income depends on making sales. High gloss floor tiles especially for bathrooms are not ideal since they lack grip once they get wet or when the bathroom is moist after a shower.

I agree with you the pillars are unfortunate. The replacement tiles will stand out no matter how close they come to matching so you're better off making sure they are clearly different so the gray one is better. Putting busy mosaic tiles could look nice but will interrupt the flow between rooms which I'm guessing is your problem with the columns in the first place. You will need to create a dextrous solution to tying into the 2x4 wall on the left side but I think it can be done tastefully- maybe beveling it back once you get past he end of that wall.

Love blue tiles. Depending on how much sun and how hot your pool gets in the summer should dictate what color it is. We live in Arizona, so cool blues work best. Our neighbor has brown tile and a dark pebble tech pool. Looks like a swimming hole and gets really hot - 94% water in the summer. They obviously didn't think it through.