WebRTC doesn't do everything for you; it's really just responsible for tying together ICE with media streams. Signaling is up to you to figure out. For instance, multiple clients in one room: this is part of the signaling layer and is not WebRTC's responsibility (I built this into zonko.chat if you want to see how it works though).

Closing and restarting connections is signaling layer stuff, ie your responsibility.

Echo cancellation is really supposed to be application layer and up to you as well, but I think this will probably shift to be the browser's/WebRTC's/getUserMedia's responsibility at some point.

Re. TURN: ICE is the process that works out whether a specific client needs to relay through a TURN server. The question is: do you need to implement a TURN server? The answer is: yes, you need a TURN server. If you built a P2P app that you want to work for all users, you will always need a TURN server. You can run coturn on the same box that you serve your app from. Most likely a side project will never hit the scale requiring more than a $5 digitalocean box for TURN.

And yes, it should not be a surprise that products are time consuming to build :) WebRTC is plumbing; you probably were expecting something more like Jitsi.