Personally, I hate it when people answer a question with "why would you do that?" or "why don't you do this instead?"
But since you already got an answer to your specific question, and since I was in the same situation a year ago trying to cut energy consumption, have you considered using something like this:
https://www.amazon.de/gp/product/B08TC2 ... UTF8&psc=1
Apologies if linking to Amazon is bad form, but this is the exact product I bought, and besides, it seems like it's been discontinued, so it's not exactly advertising.
Last year, I simply went through the data for possible low-watt mini-PCs that I could use to replace an old i7 Mac Mini Server from 2011. This beast sucked 85 watts just for the machine when at full throttle. Add the thunderbolt-to-USB dock and external drives to that, plus the extra internal drive, I was way over 100 watts.
The Intel J4125 CPU machine I linked to above eats 10W at max utilization. And on most parameters, it's as fast as my i7 Mac Mini Server from 2011. I would probably look for something newer, though, and also that particular mini PC can't even power a single 2.5" USB HDD via its USB port, so perhaps there's a better one out there.
Most of these come with Windows if that's what you prefer, but personally I installed Linux Mint on mine. In my experience, I've been unable to get Windows 10 to properly spin down external drives when idle, but in Linux, smartctl is bloody awesome - I can set every parameter, so I have all drives set to spin down after five minutes and use max power management (except for on Seagate drive that seems to ignore all my commands - all WD drives behave well). And I control what gets to spin up those drives, so when they sleep, the stay asleep until I access them. And 2.5" USB drives are extremely power efficient, so if you're okay with a 5-second lag waiting for them to spin up, you wouldn't need the SSD to cache them anyway.
If you wanna go even more extreme - and have a lot of devices... I have this MiniPC plus four 4-port powered USB hubs capable of supplying power to my 16 USB drives, and I got rid of all bundled PSUs and replaced them with an old 200W Dell ATX PSU that it useless for a new desktop build, but extremely power efficient and idles at about half a watt. With my system just downloading torrents using the internally attached 2.5" SATA drive, and the 16 external drives sleeping, I'm somewhere between 5 and 10 watts total usage. And everything is online, just with a 5-second delay for access.