You will probably not have a great experience running cctv from a pi. You may want something a bit beefier unless your cams are low res, mostly due to transcode/copying costs.

In terms of disk, you want multiple disks as either raid/zfs/btrfs/lvm. It will probably be better to do this on a separate machine and mount it via nfs.

For your boot volume, you can also use a usb thumb drive to help avoid sd card fatigue.