Very interested into seeing how you further progress. A friend of mine and me were facing similar questions concerning the choice of hardware. While he went for a N100 ITX build I decided to take the much less foreseeable route of going with a SBC.
Why? Mostly because I wanted and I like to tinker. Already running ARM on the desktop I also really wanted to do the same for my home NAS.
I did not consider the Pi at all though but got pretty much fixated on the rk3588 SOC as it provides far better IO: A combo PCIe 2x1 or S-ATA port, a PCIe 3x4 M.2 socket and a 2.5Gbps NIC. Equipped with those capabilities and performance which is comparably to the N100 I took the plunge and went for a RADXA Rock 5B.
Although we talk about single figure wattage improvements when idling those are still pretty substantial: 8W for the N100 when idling (running Arch Linux, no storage) compared to less than 1,5W idling (running Debian, no storage). For more resource intensive tasks the N100 easily breaks 30-40W while the Rock 5B is just fine with a 5V 15W power supply. That said the power draw does not yet factor in the idle power consumption of the PicoPSU which will power the S-ATA drives (and the SBC) or the M.2 to S-ATA adapter in the final setup. But I don't think that this will exceed 2W. Even adding those to the bill should still result in around 40kWh a year, when purely idling.
So while the N100's 6W TDP does not even reflect the idle power consumption when measuring the total system power of the mini ITX board, RAM, the boot medium, NIC and a high quality PSU the Rock 5B is almost on par with the performance per watt metrics of Apple Silicon.
The setup is much more involved though. As the hardware is still fairly new and much less standardised than the x86(_64) environment, it just now received solid kernel mainline support (6.7 rc1) and while the GPU and video decoder acceleration is great by now it hasn't yet trickled down to all projects. For instance the Jellyfin docker image (due to ffmpeg) still needs some modifications.