True, but a VPN can be used to mask your real IP address because all of your network traffic is relayed through another computer with a different IP address.
This is true, however you still leak your IP address to that VPN provider anyway. So it comes down to who you trust, your ISP or your VPN provider(s)? 😅
In principle, yes, but they don’t need to be able to communicate directly as long as both clients can communicate with a TURN server. At least, that’s how I understand it.
Actually I think you’re right, STUN/ICE are specifications for services that allow two or more peers to figure out what their direct IP addresses are so they can communicate in a p2p fashion, whilst I think TURN is a specification/service for peers to communicate and exchange (generally) media through a central server.
You still leak your IP address with that TURN server however.