My 2 cents... Not a terrible article, but does touch on points to think about. Definitely read the RAID article link as well.
direct attached or network attached storage (NAS)?
How do you see yourself using the new storage you are planning to purchase?
Will this be used portable or just in your office only?
In either case (direct attach or NAS) you can have multiple drives in an enclosure, unless you go with a high capacity USB external drive single drive device. Typically those drives will be configured by you to act as one large drive. You will need to pay particular attention to the RAID formats you can use and the pros and cons of each specification. This could be very important when you begin to have more than a few drives. Take into consideration speed of operation (reading and writing to device) and fault tolerance (if one drive fails, what happens to the data?).
Neither storage solution will negate having to backup your data regularly. So make sure that you consider this in your planning and add into your workflow.
I use a Synology NAS for data backup and have been pleased with it. I would recommend choosing from their small to medium business product line should you decide to venture into using a NAS.
Good luck with making your choice!