I think the tile you have selected sounds lovely. I am wrapping up a bathroom where I replaces 4x4 tiles with 12x12 tiles and I love the look. It minimizes grout lines and maximizes the focus on the tiles. I also agree that big tiles can make the space look larger by not breaking up the space quite so much. As long as the thinset properly bonds, there should be no concern of tiles falling. There are some tile experts on this site that might have suggestions on techniques and/or products. I believe your concern of cuts should be mostly resolved by a good tile setter. I would recommend specifically discussing this concern with your tile setter and asking him to share the layouts for your approval. I believe (from reading and minimal experience -- I'm not an actual expert) you want to try to avoid laying cut tiles that are smaller than half the size of the tile. I believe in most cases this should be possible, but it certainly takes some work up front to plan the layout.

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.

Ok. I have an idea! First of all let’s do a sliding barn door on the outside so we save on some room. Then I think you do need a bathtub. I totally agree with your family ... but! I’ve seen a standing tub in a shower. I’m wondering if this can work in this small space. I’m going to try finding pictures.... but I think as big as we can make the shower we can try to see if a tub works also. This is to maximize the space you do have. Am I making sense?

Help us help you. Pictures? Inspiration?