If you’re running unRAID as your NAS/server OS, then you have the benefit of running a variety of different drives, just adding them as you need them. unRAID is designed to use regular consumer drives. I wouldn’t worry about buying drives that are labeled as “NAS” drives. Better to buy, as seanho posted, used enterprise grade SAS drives from eBay, or shuck the drives out of EasyStore, WD My Book, or WD Elements in sizes 8TB or larger. There are many, many posts on Reddit and elsewhere that the drives in these three brands in 8TB or larger sizes are either WD Reds or white label red equivalent or enterprise/data center drives. JDM has a video about shucking on his Youtube channel. There are also a bunch of other such videos a search on Youtube will find.
As for continuous spinning or spinning your drives down. There are two camps: 1. spinning drives 100% is better to save wear and limit drive failure; 2. spinning drives down will not adversely affect the drive within it’s working lifetime. There’s obviously a lot more to it than that. But that’s the gist. I used to leave my drives spinning 100% but as my array grew, I have adopted drive settings that tend to have my drives spinning up about 1x per day. I believe the key is avoiding drives spinning up and down often throughout the day.
seanho makes a great point about being sure to run parity and to have backups of important data. These things are far more important than what color the drive is. Also, keep in mind some of the info from drive companies is marketing and doesn’t matter. For example, WD Reds have TLER. I used to see a lot of stuff about buying WD Reds because of TLER. Then I read this post from the inventor of unRAID.
And if you are concerned about energy consumption, better to focus on running fewer, larger drives (greater density) and running drives that spin at lower rpm (5400 rpm). More drives equals greater power consumption; faster spinning drives equals greater power consumption.
If you follow seanho’s info about backing up and buy used enterprise SAS drives, or shuck 8TB or larger EasyStore, WD My Book, or WD Elements, you’ll be fine.