how far apart to place brackets
Most manufacturers include directions for spacing of standards for various load weights and shelves of different lengths. Supporting brackets for most shelves should be spaced no more than 24 inches apart for light to medium loads (15 to 20 pounds per foot). This means that the vertical slotted pilasters must be spaced at about that distance from one another on the wall.
However, for heavier loads (30 to 40 pounds per foot), you will need brackets closer together to keep shelves from bowing, usually 16 to 18 inches apart, so pilasters will also have to be spaced closer together.