It's been done. The "this is all true" gimmick has been used countless times by different authors, and that's too similar to other ways I've seen it presented. If you want to give your book a "this is all true" spin you might need to find a different way of introducing it if you want it to engage interest. Remember that your reader is going to know damn well that it's just a gimmick; you've got to give them a good reason to want to suspend their disbelief. "Because I say so" isn't enough.