I don't remember it is 5v or 3.3v but you can use as power pin. Try it !

I powered to Arduino, and get power from Arduino to power to both bread board. Arduino has two GND pins, 5v pin, 3.3v pin and IOREF pin, you can get power from them

To exchange data between server client, it need to have a TCP connection (called TCP socket) between them. When you type IP address or domain name on web browser, it creates TCP connection to web server and then send an HTTP request via this TCP connection. When receiving HTTP request, Web server sends HTTP response via the same TCP connection. When receiving HTTP response, Web browser will close the TCP connection, it's not able to exchange data between client and server any more unless we reload web page again. To update data, you have to reload page again and again. Reloading webpage not only increase data traffic but also increase delay. On the other hand, if server can not send data to client if client does not make any HTTP request.

What if we use websoket? The second TCP connection is created between web server and web client (web browser). The TCP connection is kept unless you manually close it or network is dropped. Therefore, data can be exchanged between server client anytime.