I don't auto create rules, but I do know users are auto-created when they login with a valid IMAP user/pass (that's what it uses for authentication).
I'm not very familiar with PostgresSQL. I've only used MySQL. I didn't want to tamper with Apple's install of it, have problems with Apple's version of Roundcube using it, or install another instance of it, so I went with MySQL.
This is an automated installation of Roundcube.
It configures postgres, initializes the database, installs mcrypt, configures managesieve (vacation filter)
configures roundcube defaults that should work for most installations (sets default folders, reply hostname, etc)
and installs a Roundcube WebApp.
About 2 minutes to install, at the end it will load your default site (/mail) with Rouncube displayed.
With Roundcube setup as a webapp, you can enable/disable it per site via the Server app, Web, Site, Advanced Settings (you will see a new "topicdesk-Roundcube" webapp