As an anecdote: I have one system (x86) with pi-hole and unbound in a docker, and a secondary raspberry pi with pi-hole running on bare metal. The docker system (although much more performant in general) has a lower latency as the raspberry bare metal install.
I have all these services in docker as well (although not with the docker compose file here) and they run perfectly fine with a very low resource footprint.
I am currently also looking for a 10“ rack.
Where did you get this one? It sounds like you are from Germany (at least according to the sticker) and so am I.
Who needs a domain anyway