The current gen processors are hilariously efficient if you build the rest the system properly. I will warn you that the low watt rabbit hole gets crazy. Simply changing a component from one slot to another can make a large difference on idle power draw. mattgadient.com/7-watts-idle-on-intel-12th-13th-g… is a nice write up on a low power build that lists some of the things to consider when it comes to power usage and CPU idle states. At this point, I would stay away from server hardware unless you have a specific reason to run it. It may be cheap to buy at first, but you end up paying a lot more in the long run on power usage. I would also recommended you look at unraid. It has a somewhat proprietary raid format that does the parity calculations on the file level and not the block level. The result is that unraid is able to keep drives spun down and off much more aggressively than a traditional raid setup. It only needs to spin up the drive that has the file and not the whole disk pack.