Why create another app for that? There are already several apps available that can read ePUB, also DRM restricted.
You will need Adobe software to put the DRM on the books, and that is not cheap. Also, it is rather useless since it can be removed in milliseconds. Also keep in mind that converting Word/InDesign/PDF to ePUB takes a specialist to do it right. All of the automated tools will deliver questionable results with unpredictable output on the various readers.
Security will be an issue, but nothing that can be solved. Having a good SSL certificate will help, but good quality code is also very important.