1: That fact is that tile size is a personal preference to some degree. Depending on the space of the room and the continuity of the room flow, depends on how
    a 12" tile versus an 18" tile would look. With regards to the labor cost, larger tile requires more physical labor to maneuver and install, therefore resulting 
    in a higher installation labor cost. It's not huge, but costs more. Material cost is a little higher for larger tiles as well. As a rule of thumb, "larger space, 
    larger tile size", "smaller space, smaller tile size". I hope this helps.