Bitrate Is the Starting Point
A 128 kbps stream sends approximately 128 kilobits of audio data per second for each listener connection, before accounting for protocol overhead. Higher bitrates require more bandwidth.
Listener Count Multiplies the Requirement
The more listeners receive the stream, the more total outbound traffic is required from the streaming service. This is one reason a hosted SHOUTcast server is different from broadcasting directly from a home computer.
Your DJ Upload Connection Is Different
The DJ encoder generally sends one source stream to the SHOUTcast server. The server then distributes the stream to listeners. Your local upload requirement is therefore not simply your bitrate multiplied by every listener.
Choose a Sensible Bitrate
Select a bitrate appropriate for your audience, audio source, and service plan. Higher bitrate can improve quality, but it also increases data requirements for listeners and the service.