Also, I'm not targeting consumers. Since the engine is already opensource, I don't have a problem making the whole app open.
"I would personally pay for is the ability to have my custom designed notebook printed and shipped to me" -> I think the core feature is how easily you can design your custom notebook. There are already p-o-d services and you can just use Photoshop or Word for editing. But they are too complex.
What I was trying to say is that, maybe, some companies would pay for custom widgets that hook to a db and display nice graphs & tables to quickly create business reports. But I don't think those companies care about p-o-d because they already have their own providers.
So far, the business model is: free everything except for the cloud storage (if any) and premium widgets & layouts. I would not add a premium over the p-o-d price since I have no control over the quality and I would offer it as a 'bonus', like an option to link the app to a 3rd party printer of your choice.
Anyway, thanks for the input, it really helped me! If you want to keep in touch, let me know.