Does anyone have any links to resources or suggestions for building a streaming or realtime api like twitter firehose, facebook updates realtime api, instagram real-time api, etc in Node.js?
I helped develop the DataSift streaming API and I've been working on a node module for easily creating HTTP or WebSocket firehose streaming API's out of any data source you like. https://github.com/ollieparsley/node-firehose hope you find it useful.
Your question is very broad.
Maybe you are looking for http://socket.io/ ?
When it comes to Web APIs, a good understanding of REST is helpful before going anywhere complex.