Why would you need to create your own app? Ebooks come in 2 standard formats, Kindle (.mobi) and ePub. There are lots of apps that can read those formats already.
You say "I will take on the responsibility with getting the publishers to provide me the e-book version of the books", but if the publishers create an ebook, why would they need you to make it available, when they can send it to Amazon and/or B&N, etc.
People's ereaders will not be able to access the books if you create your own DRM or format, and they will not like that. You would be missing a vast amount of the market.