Besides RAM, what resources do for think you’re saving? Not CPU cycles or IO ops, because you’re processing the same amount of DB queries either way. Not power consumption, since that isn’t affected by RAM utilization. Maybe disc space? But that’s even cheaper than RAM.

Or more importantly: the extent to which you can self-host out of sheer luck and ignorance like you suggest is very limited. If you don’t want to engage with a minimum amount of configuration, you might bump into security issues (a much broader and complex subject) long before any of the above has a material impact.

You’re mischaracterizing what I said. My point is that running multiple DB processes on a server isn’t going to have a significant impact on system load, if all other factor are kept constant.