You can use firebase to skip backend programming, or even user firebase to setup a nodejs backend (functions) . The bad thing about not using a backend is security, you would need to master firebase security rules to completely protect data.
Read moreShould I create my own backend?
Conclusion: Unless your app is very data intensive then you won’t meet any of the data caps. Firebase will help you get your app online quickly and cheaply before scaling excellently once the users start pushing the upper limits. NOTE: I would never recommend someone building their own backend when starting a new app.
Read more