If you're a 'startup', you'll never need any of that work until you make it big. 99% of startups do not make it even medium size.

If you're a small business, you almost never need replicas or pooling. Postgres is insanely capable on modern hardware, and is probably the fastest part of your application if your application is written in a slower dynamic language like Python.

I once worked with a company that scaled up to 30M revenue annually, and never once needed more than a single dedicated server for postgres.