If you choose to go with Matrix, I would strongly recommend you to give the Continuwuity server a try. It is quite simple to install, much less resource-intensive than the commonly-used Synapse, and has an active community behind it.

apparently, I need a TURN server to get this working properly

Do note, Matrix recently has a new calling stack called MatrixRTC, and for that you would be setting up LiveKit in place of a TURN server. That also opens many ports by default, but I think there is a “UDP mux” mode that listens all on one port. I’ll be looking into it soon.

The other alternative is XMPP, which is a bit more complex to set up (more ports, non-HTTP protocol, more subdomains, various opt-in features) but is generally more lightweight and fast. ejabberd is my choice, but people tend to like Prosody and Snikket as well. While they use the traditional TURN servers for calls, their clients could use a lot of improvements though…

So yeah, my Continuwuity and the XMPP server sits on a small homelab machine, and with some extra tuning and grit, they:re totally federable. LiveKit and TURN sits on a VPS for better network performance. To be honest, I do all of this mainly because I wanna talk to cool people on the internet, so the service has to be federatable.