What are the pros and cons of using Postgres over SQLite for tiny and small projects?
The main differences will be the features you need, for the applications you'll be developing and their use cases. It sounds like if your PostgreSQL instances are only consuming up to 200 MBs of memory at a time, you already have tiny databases, and it doesn't really matter too much if you choose one way or the other due to data size, rather it'll be more feature specific which as you realize SQLite is a much simpler database lacking a lot of addition features a full RDBMS like PostgreSQL has.
Personally, I'd say unless the environment you're working in / hosting your data on is constrained to use SQLite like mobile development (because of its portability for offline storage) I'd opt for a full RDBMS system by default.