Depends on what you load onto it. It has backup software that comes with it, but you don't have to use it. You can format it to be just another external drive if you want
Could this be used to not only store music files on, but also to use as the primary drive for an itunes set up so that it does not store the music on your in computer hard drive?
I copied some movies to it and watched bits from it fine so music should be totally fine speed-wise. I was using USB 3.0. I don't think i-tunes would have an issue but it is finicky software.
Yes this is a Awesome storage item I have thousands of music cd's on mine drag and drop them from My Book to wherever you need them to include I Pods and Mps players and all Laptops and Computers.
Yes. USB 3.0 is backward compatable. You may get a notification from your OS that a component is not running as fast as it could be, but it will run fine.
12v dc @ 1500mA. Most external units use the save voltage, just different power adapters and plug in tips. I've successfully used the WD, Toshiba and Seagate Power Supplies to operate my external drives.
Yes. It can be used with any OS. You may want to remove the WD software on it to gain a little more control over the unit (simply format it once you receive it). The built in software is useful if you want to use it to run backups, otherwise, it simply gets in the way.
The PS4 does not support playing games from an external hard drive. You are able to upgrade the internal drive and there are many guides online with instructions on how to do that.
The reason not many are answering on PS4 is because PS4 does not support external hard drives for game installs so unless you need it for movies or music its useless on PS4.
Now you can replace the hard drive in the PS4 without voiding warranty so the next best question to ask is if the HDD in this external enclosure fits in a PS4. Wish I could answer that one for you but im not sure I use XB1 for everything and PS4 for only exclusive games so havent needed more space on it.