Implementing Audio chat with Socket.IO and NodeJS
If I were you, I would use a WebRTC library providing both the client and the server side. Check EasyRTC, SimpleWebRTC, PeerJS or others. Most libraries are implemented in Javascript and run in Node.js.
You will find tutorials in their respective websites.
I personally use PeerJS, the code and documentation are both very good, and it fully supports data channels (useful for file transfer). The only thing is that there are only 2 founders, and the community seems quite small.
I am also planning to make your kind of app on nodejs. During my research I found that WEBRTC support for mobile browsers is limited. In todays world whenever we are building a Web app we consider that a major portion of our users are going to use it on mobile phone. WebRtc is supported on android browsers like chrome, Firefox and opera. But on iPhone it doesn't support safari nor windows phone browsers.You should take a look at Wowza streaming cloud at https://www.wowza.com/docs/wowza-streaming-cloud-free-trial