Crowdbotics currently (April 2019) provides two different architectures for people building React Native apps. You can pick either one depending on what you need.
The RN-Expo scaffold uses Expo as its frontend framework, which lets you immediately access a working app on your phone using the Expo toolkit, without publishing to any app stores. The backend is a set of Django REST APIs, hosted on Heroku and supported on a Postgres database. It comes with login, registration, email confirmation, an admin panel, and API connections all working out of the box. Django is a wonderful and scalable backend, but requires you to work with Python.
If you’re not sure which is right, we recommend picking the RN scaffold (Firebase) – it’s got more ready-to-use modules available from the Crowdbotics library. If you know Django and love it, or if you really need to use Expo, then you can go with Expo.