The short answer is that you must identify the minimally viable product first. The way to reach this MVP is not easy, but you must do it in order to keep focus and build the most important thing at the start.

As for libraries - You wish to avoid re-inventing the wheel (as it's not moving you forward vis a vis your MVP). So invest time and research for SDKs/Libs that can boost your productivity.

Other good rules to follow: 1. Build a user testing focus group and see if your ideas got a true connection with reality. You will learn A LOT from this. 2. Plan for multiple releases - Don't try to do too much for the first release. Iterate quickly and build your service/product in layers. 3. Measure and analyze your users' actions - It will give you a powerful tool to decide what to do and how to improve your releases. 4. Monetization plan - https://greenido.wordpress.com/2015/07/31/app-monetization-c... (disclaimer: this is a course I've helped to build)

Good luck!