i have a similar project on my todo list. But i have not received all the answers i had requested some time back. I appreciate this is mainly do to C2 being a 2D Game Engine and interactive books apps are undiscovered country for Scirra. As for large background images - maybe 1024px or higher for iPad Retina etc, and assuming you'll need at least 20 full colour pages as PNG's, plus spritesheet animations, text objects, interactions, particles, scene transitions - i think it will choke on many devices at the moment. My own research has revealed that the best interactive children's book apps for iOS and Android, are being developed with pure Objective C, sometimes with a framework like Cocos2d for iOS and Cocos2d-X for C++ devs who can deploy to both platforms. Neither is Flash DEAD as many believe. It's not! Many books are coded in Actionscript 3.0 and developed with the Starling Framework and Box2d or Nape with GPU accelerated blisteringly fast graphics - something HTML5 cannot yet compare with.
But i am still going to try either C2 or Stencyl in the near future as i want to learn myself and be 100% indie. I love the HTML5 for all devices - it's so democratizing - is that a word? - but still has some way to go.
I am presently learning AS 3.0 because i love Starling and Citrus. But i am struggling. If i get kickstarter funding for my book, i might just get a developer on boards. But up to now, nobody has been able to answer my questions because there isn't a book app out there on the app store made with C2 or Stencyl that they can use as a benchmark for comparison.
Here's hoping a few C2 devs will see this and enlighten me.