Backing up suggestions for the ZxBackup

I am using ZxBackup and the local filesystem for my Backup Path on my mail server (mail:/opt/zimbra/backup/zextras). Is there a suggestion about how to handle system backups? We back up online, to an NFS file system.

• Should I put a cronjob to regularly rsync the contents of mail:/opt/zimbra/backup/zextras to the NFS filesystem and how often should I run this? Is rsync -while the server is running- going to leave the backup in an unknown state and make it un-restorable?
• Should I just depend on the regular (tar and rsync based) filesystem backups (weekly full, daily incremental)? Will I be able to recover "rolling-up" incrementals to the latest full or I can restore only from the latest full backup?

Thank you!
George