Have anyone used following scenario in Zimbra OpenSource Edition?

Two Zimbra SMTP servers will be installed for high availability.

These two SMTP servers will be mapped to two MX records, primary and secondary.

Two Zimbra Proxy will be installed. Each will have their own alias mapped on internet.

Three Zimbra front end will be installed. Each front end will be configured to act against two Zimbra proxy servers.

Two Zimbra LDAP servers will be installed, primary and secondary.

Two Zimbra Mail stores will be configured.

Both Primary and Secondary LDAP servers will be configured to authenticate with Active Directory. This needs to be done for High Availability.

All Zimbra services will be LDAP Authentication.

Please provide feasibility of this scenario and suggest improvement paths.