launching new stories from a home screen is possible by creating a home page and removing the motion controls, leaving only clicks to link to the desired stories.
Regarding your second question, you cannot have in-app purchases since the pubcoder export could be a book or a single application, so you can sell those export formats.
Let me be clear: by creating the app using PubCoder you are able to sell it in the stores but not with other content within the app.
The best solution is to create one app from which you can sell more books, we have Shelf , which is basically what you need.
Shelf is a library app that allows you to sell your books with the in-app purchase system, or subscription or distribute those for free.
If you are interested please contact our account manager email@example.com