I used this approach to drive entire app, and it works. Nearly all data are fetched from SQLite. User can select a database, which can change app views, and the data. In my experience it is quite fast.

My example for android app:

https://f-droid.org/pl/packages/io.github.rumcajs.offlineweb...

Note that I am not android experienced programmer, and I am still learning.

No. SQLite doesn't have users, proper views, row level security, proper foreign keys, or functions.

Yes. I already did that once though, so I skip that step now (unless ofc it's a SQLite usecase).

Not really. They are two different paradigms. Use the one that is right for you.

SQLite is embedded for local applications with one writer mostly.

Postgres is for a client-server architecture with many writers.

When you start a project, you generally know which architecture you need.

In a lot of cases using SQLite means you write queries incompatible with RDBMS. No need to worry about race conditions or the amount of queries you make, when 100 selects are uber fast.