I have 2 hp g800 sff i5 4th gen @3.4ghz a qnap nas for storage, 2 rpi 4 and an odroid m1 as a docker swarm for all my services a modem a router and my switch and I’m having around 100 watt usage for the whole cluster.
So i think an SFF pc will do the job fine and meet your power and computing requirements.
Looks great, unfortunately i’m running on docker swarm. Hope it’ll support that somewhere in the future so i can use it. As i’m a great fan of uptime kuma and use it for work and private.