Leo advises to buy multiple smaller hard drives over one extremely large hard drive. The bigger the size, the higher the error rate...which can be catastrophic in the worst case scenario. In any case, move away from old spinning drives to faster Solid-state Drives (SSD), where the cost per gigabyte is getting conveniently cheaper. You may have so much storage in the future that you could forget to discipline yourself on cleaning out files!
It depends on how the array backs up. If it's using a proprietary system to combine the hard drives, he'll have to get a duplicate enclosure to the one he had to read the disks. If it's using a standard system like RAID 5 or RAID 0, he may be able to use another RAID box to put the drives in. Leo says he won't be able to read the drives at all unless he has something to duplicate the setup it was using. He'll need to get another enclosure identical to his previous one so he can read the drives.