Just be real careful with the chromebox, an lot of them can’t run Linux and are pretty low specs so I wouldn’t want try putting everything I want to run on them. The CPU in HP gen 2 one I have is just a dual core without hyper threading. I would only even look into the a Chromebox if your thinking about Plex pass and hardware transcoding.
Also should be noted anything bought used your not paying for a Windows license though most the SFF boxes come with windows license baked into the bios.