To elaborate on Daniel's comment...
If you can get by with just using Firebase (and you usually can!), that really simplifies the back end situation, because you generally don't have to write a backend... you just write asynchronous front-end code that queries and stores data in the database.
If you really do need some code running on the server-side, you can probably do that with a couple short Firebase cloud functions.
I strongly encourage teams to use Firebase, because it (usually) makes persistent storage of data simpler, and it handles basic authentication and security too!