Hello,
Setting up RAID when using ZFS is fairly straight forward using the FreeNAS GUI. Speaking from experience (both good and bad!) I would recommend "trying out" FreeNAS in a virtual environment before hand so you can get a better understanding of how it works, how to configure "stuff" (storage, networks, CIFS, NFS, iSCSI, etc, etc etc). This way you can make mistakes in your config, test things out etc and not worry about having to rebuild your physical environment; at least in a virtual environment you can do a "snapshot" of the virtual machine prior to making big changes and revert back to a good config it it all goes pear shaped