Custom Sticker sheets are never not a good idea, as you can see by this recent project we ran for Nicky Davis.
Normally a sticker sheet is roughly 5" x 7" or similar size, with 4 - 7 assorted graphics. In this case, the format is pushed to new limits at a size of 8.5" x 11", featuring 4 gargantuan graphics. Sticker Sheets are an incredible way to combine art and create an incredible final product. Remember to experiment with sizes, layouts, and shapes for wild results.