With this many applications I would be looking at getting one higher powered server and running docker on it. Would be more power efficient as you only need one OS and one PSU as well as likely much cheaper.
Docker has a multitude of benefits for single machine multitenant deployment strategy, namely resource and file system isolation.
It also has the benefit of being self documenting of dependencies via layers, which is a nice thing to have. To be honest, running just about anything self-hosted can be deemed overkill when there are so many free hosted solutions. But that’s why we’re engineers because sometimes it just scratches an itch for us :)
Docker is not overkill at all. Having 20 servers to run a few very low utilization is overkill. When you run a whole bunch of stuff on the same server it becomes a lot simpler than installing them the traditional way. A lot of self hosted server software is not in the repos so you end up having to add extra repos and after you do that a few times I find that something always ends up breaking and ruining the whole OS. Its much simpler to keep the host os basically stock debian with docker installed and then if anything goes bad its contained.
