Maria is soooo talented. She taught a True Colour Expert course in Toronto last year that I attended and learned so much from. Now about your 18" x 24" pictures: 18" x 3 = 54". If you have a double bed, which is 54" wide you would be fine, because you'd be adding about 3" between the pictures and they would extend past the edges of the headboard just like Maria's pictures do. If your bed is queen size, which is 60" wide, you'd still be ok if you spaced the pictures out a little more. And if you have a king size bed, 72" to 80" wide, then you might want to add a fourth one to get this extra wide grouping look.