Looking at this list:

    Standard Postgres compiled with some AWS-specific monitoring hooks
    A custom backup system using EBS snapshots
    Automated configuration management via Chef/Puppet/Ansible
    Load balancers and connection pooling (PgBouncer)
    Monitoring integration with CloudWatch
    Automated failover scripting

Every company I've ever on boarded at, that hosted their own database, had number one, and a lot of TODOs around the rest. It's really hard! Honestly, it could be a full time job for a team. And that's more expensive than RDS.