It is helpful to page out/dummy a story when you are writing it, but the illustrator may do it differently, and your page count might not be 32 pages. Also, there's different ways to page out a 32 page book (end papers or no end papers change the page count).
So, if you're not illustrating and doing a storyboard or dummy helps, go for it! But just know that the illustrator might pace it differently, or the publisher might have a different page count or layout than you do.
For reference, the book I just illustrated is 40 pages, plus a gatefold, so it works out to 44 pages. Also, the end papers and back cover tell part of the story, so every page is used, and there's very little text (don't have actual count, but I think it's under 100 words, and a good portion of that text is the names of the two characters).