Augure, let me just address your first question for now to let you consider the implications before you even delve into the other questions.
So I hope you’ve read the info on WD’s website and have learnt that this is a NAS product. Which means that it is not meant to be directly connected to your computer - it is meant to be directly connected to your network and is hence called a NAS (Network Attached Storage) server. This product is essentially a lightweight computer running an embedded Linux OS called BusyBox under the hood and provides a web interface, called the dashboard, for all common disk and user management operations.
If you are looking to simply get a hard drive that attaches to your computer via USB then this is not the product - as the USB ports on this product is not for that purpose. This product will have either two hard drives already when you buy, unless you buy the diskless version, in which case you have to buy either one or two hard drives and put them in yourself (a very simple tool-free task). After that you plug this into you LAN by attaching a ethernet cale from a router or switch to this unit. And you can then access all the storage on the hard drive from anywhere on your network or from outside your home/small-office network over the Internet via the various ways it provides access. The simplest and most consumer-friendly way to access this storage is using the My Cloud app available for computers and mobile devices.
So if you are looking for an external hard drive that attaches to your computer you will need to consider WD’s My Book or My Passport lines of products or some other vendors’ similar external USB hard drives. This product is a small NAS server that should be compared against other competing NAS servers offered by Synology, Seagate, Netgear, Lacie, Buffalo Technology, etc. to see if it fits your NAS needs. Read some reviews from CNET, PC Mag, AnandTech, etc. by googling this product’s name to get a better understanding of it’s capabilities and determine it’s fit for your needs. If it does fit your needs, then consider researching further the answers to your other questions.
And by the way, the USB ports on this is meant to add additional external hard drives etiher in addition to or even without any internal hard drives you have in this product. That’s the ONLY purpose for the USB ports on this box.