Yes, trying to take all features and functions is a mistake. The key for a mobile application is to focus on 4-6 key functions/capabilitie that the business wants for a mobile application. You need to build out a MVP (Minimum Viable Product) plan with the business users. Based on that plan then you can design the end user interface and revalidate. I have seen people try to enabement everythign and it fails at the end of the day.