1. In fact, the connection will pass through TURN in a few cases (but still present). Mainly when a side is only IPv4 and where UPnP is not available.
Running a TURN server is easy (coturn), the only thing to be sure is that the server is running outside the network of a peer (to get the good public ips). I did some docs here https://git.jami.net/savoirfairelinux/ring-project/wikis/tutorials/file-transfer#using-another-turn-server
2. Also possible to run a different name server (or simply host a JSOn file) https://git.jami.net/savoirfairelinux/ring-project/wikis/tutorials/file-transfer#using-another-turn-server