You zero the disks before or not zeroing them.. dosen't matter
While you initialaize the controller using Option 4 from boot menu, it will select & assign the disks (usually 3 disks) and zero them again,
before creating an aggr, then creating the root volume.
Depend on the ontap version you choose, the remaining disk can be auto-assigned by the controller (but you can always change it)
Normally i connect only the shelf, where i want my root aggr and complere the initilization process.
halt the controller and then boot the controller to maintnanace mode.
Once controlelrs are in manintnance mode, ill complete the remaining SAS cabling (depends on the number of loop needed)
and then complete the disk assignment on each loop.
Once all the SAS cabling is according to the recommendation, reboot the controller to do the remaining configuration.
Remember to change the environment variable "bootarg.init.boot_clustered" if the controller was previusly used in 7-mode.
To make things lil easy, remove all disks ownership before you disconnect them from 7-Mode controller. (if it was previously attached to 7-Mode controller)
Please let me know, if i can provide additional information.