We always recommend using two hangers and hooks per picture, so estimate the likely number of pictures you'll be displaying at any one time and multiply by two. Bear in mind that hangers and hooks are always readily available so you can always order a few more if you need to. There is no minimum order or restrictions as everything is sold individually. If you have more pictures than you could ever hang at once, and they're mostly of an average size, allow four hangers per 2m rail. You may want more hooks than hangers as you can hang pictures one above the other on the same set of hangers.