Well, using OS X is inherently safer than Windows. Also, you'll be administering the site, not the ISP, meaning that you can adjust settings, such as firewall, to minimize intrusion. The program Little Snitch: "informs you whenever a program attempts to establish an outgoing Internet connection. You can then choose to allow or deny this connection" so if someone gets thru and tries to, say keylog, you'll be informed and can disable it.
I must confess to being curious about what on earth makes people so abusive to your enterprise. Cyber-vandalism is just unacceptable.