I am about to migrate to a new server, and with this I would like to use a different mailing system. I have concidered moving to google with my mail, but we don't want to make the expenses for this.

Zimbra seems the perfect solution.

Though I still need some questions answered:
1. zimbra - Webmin
As a main server management tool I would like to use webmin (and possibly virtualmin). Do they play nice with Zimbra? Will zimbra be recognised? Will they fight?

2. Mobile calendar and contacts
A must is the mobile contacts and calendar sync. Will this be possible with the free edition of Zimbra?

3. server load
I'll be hosting:
- a website (2000 unique visitors per month)
- mail server (zimbra)
- openx (advertisement)
- ossec
- RMS (media server)
- webmin
- and all basic servers
I've read zimbra might take up a fair amount of resource usage? In the initial stage we will be hosting 35 mail accounts.
The dedicated server will be a xeon quadcore 2.4Ghz, 4Gb ram, 160GB HDD
Hourly backups.

Thanks for your replies