Not sure what the problem with Gajim was. There’s a distro package already in Arch, although I usually use the AUR packages from git. I haven’t had any problem with either of them, though.
You should be able to limit MUCs so that they’re only for local users of a server and not accessible to people outside the server. Or, you can make them invite only, require a password, etc. So there are options there.
One-to-one video and audio chat works pretty well with XMPP. I don’t think group video/audio works, but I’ve never tried. I know that’s a really popular thing on Discord, so it’d be nice if XMPP had that too. I think there’s some work toward it, but I don’t know where that’s at.