My question is which kind of disk should I purchase? A regular disk or NAS disk?
So just from my experience: you can simply use normal disks as they work exactly as a normal hard disk. I use normal ones in my 24/7 servers since a few years without a failure.
But if you have the money and your data should be really safe from drive failure, you should buy NAS drives. They are built exactly for this purpose and generate, as far as the producing companys tell us, less vibrations, what is positive for the expected lifespan of the drives.