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.
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.