I (not a professional, but logically not untalented) can only recommend the device offered here: sensible packaging, no obscurities during installation (a few steps take a few minutes, as you will quickly impatient or suspicious of new devices, but in the end all goes well) , stable connections, contemporary speed, acceptable noise, energy-saving features, ...
Devices the easy to use and to my taste visually unusually pretty NAS series WD My Cloud Expert can be purchased both in empty and in tipped versions. I would advise a complete solution from a single source. Included are then designed for continuous operation optimized hard drives of the series WD Red at a speed of 5400 per minute. The up to four shafts guarantee depending on the version a total capacity 4 to 24 TB. The version of 16 TB provides a free usable capacity of about 12TB. Except Expert there are NAS product lines with the names Consumer or Business.
From me so far all of the options of the device have not yet been tried, and in particular I use apps quite economical, but will add my text in any abnormalities and other experiences. How far you look a NAS device as a backup medium, which is of course a question of principle, I will in any case also with reliable hardware is not all my files in a cloud.
Conclusion: Any weak points are not observed, one obtains a sustainable NAS package.