Two important things learned with this first tile job of mine: Marazzi tiles are manufactured in batches with a certain "caliber" or size class. I ended up with boxes of tile from two different batches, and the sizes were off by 1/8"! Had to return part of the order and drive around to different Home Depots until I found enough of the correct caliber tile.
Next, I used 16x16 tiles on the ceiling. This was a bad idea since the ceiling was not perfectly flat due to framing. I ended up with a fair amount of misalignment between the tiles. Fortunately, grout hid this significantly, and the lighting keeps it from being noticeable in the least. But it's not ideal.
I had to cut a few holes in the tile for lighting, controls, and speakers. After trying various carbide and dry diamond cutters, I found that the only way to effectively cut porcelain tile is with wet diamond saws. Fortunately diamond hole saws are not too expensive on ebay.