Nice guide. A little warning, while WebRTC is known as a p2p tech, what few people realize before starting using it is that while it is p2p technically, you need like 3 to 4 centralized servers to make a connection between two peers. Just google TURN, STUN and ICE servers and protocols, you will also need a signaling server (usually your app) and a web server where the app is hosted. That's why most people use webrtc as a service solutions or all in one webrtc servers that are hard to customize/setup.
You don't need STUN or TURN so long as you can be certain that your devices can talk to each other directly (without NAT punching or tunnelling). They exist because it's generally impossible to create peer-to-peer connections over the internet, unfortunately. Luckily, it's not difficult to set them up - [coturn](https://github.com/coturn/coturn) is a decent implementation. The major downside is that you're going to be paying for the bandwidth of anyone who can't make a direct connection.
The signalling server, though, just copies information about each peer to the other. Technically, you could transfer it any way you like - by carrier pigeon or through js-libp2p.