I've a ton of Pi4s and one Pi5, but the ease of use, the simplicity of 1L pc's is - for the stated applications - a no-brainer to me.
For initial purchase they certainly offer much better bang-for-buck compared to the Pi4 & Pi5, but do you have any useful links to information about relative power consumption when mostly idle?
I currently have a Pi400 (back when I bought that the Pi proper was out of stock everywhere except the scalpers charging >£150/unit for even the low RAM versions, but I found a decent deal on a Pi400 kit) running as a router/firewall with a few other small bits & bobs in containers. I keep considering replacing it with a small PC like that – my main concern being running a core bit of the home network off an SSD, though also having a bit more performance (both IO and CPU) might at times be useful too, and the Pi400 I'd like to reuse somewhere it is visible for “this is what home PCs used to be like when I were a lad” nostalgia reasons. The reasons I haven't so far (other than momentum: the 400 is sat there working quietly needing no interaction aside from the occasional update and paranoia checks of the config/log/other backups) are possible greater electricity use, and great noise if the mini-PC is not entirely passively cooled.
I had a look around and there are many values out there, just under 3W idle and about 7W spinning the CPU seem like reasonable values (to get better data I might have to try properly testing mine – I've got an overly fancy USB3 cable that displays the power passing through, so I could do that at some point, at least approximately).
Figures for mini PCs obviously vary by model, but also you see a lot of different figures for the same model (some of the difference could be due to differences in storage power draw, some don't say if they have an SSD or traditional disk, and some could be differences in ambient heat affecting draw for cooling? age may also have an effect on the efficiency of fan motors) but between 9W and 15W (mostly below 12) at idle feels like a reasonable guess based on those quick searches. This is lower than I was expecting. The official rating for an Optiplex 3070 (picking a random model from the popular ones) is “up to 1.2W” which is far lower than people have measured in their own tests so I'll not be trusting official values.
Of course the PiZero or similar would draw less than anything else I've already mentioned, though to be a router I'd need to add at least some NICs to that, some extra storage (given one of my concerns is running the router off an SD card), and would lose some CPU resource (the Zero 2 is roughly equivalent to a Pi3 there?) and a goodly chunk of RAM.
Then two used/refurbished Dell Optiplex's, great deals!
Curious because for me the affordability of a hobbyist PC is offset by the cost of Windows.
Why not just use the windows trial. Or buy a license key.
Windows license keys are absolutely everywhere. Maybe check the bios from some old laptops you own?
At my university we have this massive ewaste bin full of old pcs stickered with probably valid license keys.
Though you might be better off sticking with Linux anyway.