Even better: buy an old office desktop from about 10 years ago, upgrade the ram and storage (if you feel like it) and install Proxmox. Now you can run as many servers as you want, faster, probably cheaper, and with much less hardware.
225 watts is a bit high for most small servers, but mine seems to be rather high due to the fact that I have about 18 SATA HDDs connected to it for file server capabilities.
A Raspberry Pi 4 consumes around 5 watts running at full bore, 2-3W at idle. Of course, it also couldn't handle what I am doing or I would use it.
In fact, my Home Assistant is running on a small mini-itx Intel celeron box dedicated to that because the PI was a bit too slow for my needs. But I run quite a bit of automation stuff on my Home Assistant instance. It draws around 25 watts at idle.
I have a vm for macos. I have containers for git, dav, nextcloud, etc.
only thing I would love is something like docker to build containers from one dockerfile.
Could be great as a test/dev box though.
EDIT: Just run Portainer in an unprivileged LXC container. That's what I do. Isolation, native performance, plus a point-and click web manager for Docker containers. It's absolutely delightful!
Kubernetes is a scheduler for containerized workloads.