I've been working on a couple of picture book dummies but I can never remember how many spreads I can have! I usually use Debbie Ohi's templates. Although lately I've been marking down tiny boxes in my sketchbook that are literally thumbnail sized to help me explore pacing and page turns as I work through revisions. As illustrators we do have a number of options for using those pages.
Most of the hardcover books in my own collection are 40 page self-ended. I asked around various kidlit groups and have been reassured that the vast majority of picture books are 32 pages. A browse through one of my local libraries revealed very few 32 page self-ended books but many 32 page separate-ended books but 40 page picture books were definitely not a rarity. If you're not sure what I mean by self-ended, separated-ended, or endpapers there are links at the bottom of Debbie's post that explain. I also found this endpaper Q&A with Cecelia Yung by Robin Rosenthal over at PenandOink very helpful.
My conclusion: when writing, write with 32 pages in mind. When illustrating, focus on variety, pacing, and strong page turns.
I thought I'd share what I've dubbed my Picture Book Layout Cheat Sheet - a handy little reminder of the possible options with examples that I can refer back to. If you've found other unique or interesting layouts I'd love to hear about them.