Hi.
You’ll have to excuse me for thinking that a NAS like this is most likely overkill even for your purposes. For video editor or compositor, no.
While the MyCloud I bought 5 years ago is really slow, it’s worked reliably for playing HD content the entire time. I do know that it’s days are numbered and doubt it will work well if at all with UHD content.
The biggest problem with this unit is where you’d stash it to eliminate the noise and dissipate the heat produced by the CPU and drives.
One other thought: unless you’re buying downloads, why do you not that type of capacity? Even then, as mundane as it seems, you can burn the downloads to a shiny disc for archiving. Do you need every movie you’ve ever bought instantly available? A rack of BD’s doesn’t drive up your electric bill.
My preference would be to get a 2 bay version of that unit and rock it with SSD’s.
Enjoy your new box.