Please check my existing post about my low-energy rack:
This is using a SuperMicro A2SDi-4C-HLN4F motherboard with a Quad-core Intel Atom 2.2 GHz CPU. This motherboard already has 4 ethernet ports out of the box + dedicated management port for IPMI.
The entire rack uses a little over 50 Watts, but that’s also for a switch and firewall, so I would guess the server alone uses about 15-20 Watts.
I’m running a number of Docker containers, including Home Assistant, and it still uses less than 1% CPU when idle.