its very easy to install via docker as mentioned above. Mumble is very lightweight. You could run the server on your desktop in the background easily or even on your router, there is a package for openwrt. The sound quality is awesome, voice is e2e encrypted and bandwidth should not be a problem either for a couple of people in the chat while you are playing.

There were problems like these ten years ago in Europe, but nowadays it works very well. W

They use xmpp as their messaging system I think. Xmpp is open source, but I am not sure about the licence used.

I’d say it’s best to only buy routing devices supporting openwrt. Some Ubiquity devices seem compatible, so maybe you are in luck. In my opinion it’s just best to stay away from preinstalled commercial software and just install Linux. You get away from the whole process of enshitification, gain long term support and an incredible set of features commercial software will never provide (at a reasonable price) imho.