I'm ending my testing and internal deployment in-house of Zimbra Network Ed. 5.11. We are now going to set up a live solution for our customers. I would like it to be like this:

Use my existing in-house installation as a standby Zimbra server. Buy a new server for location 2, which is going to be the main Zimbra server. My questions is:

1. Will I have to buy twice as many licenses?
2. How do I configure Zimbra to support a standby server?
3. Which OS is best suited for Zimbra? Im currently using Ubuntu Server 8.04, is this OK?