WCF Hosts. Ports and Namespaces

If you have one Windows Service host which hosts multiple WCF Services, you can reuse the same port for multiple endpoints.

If you use host the endpoints in different Windows Service Hosts then you can't share port. This is because the host is responsible for the port.

Silverlight and WCF Services

This is a pretty good article on how to expose a WCF service to AJAX. AJAX accessing uses JSON to interact with web services. In order to achieve that you need to make the service as Scriptable.

Although this article is describing interacting AJAX and WCF, the same technique applies for exposing WCF services to Silverlight. Please note for silverlight you must have the service running under the same domain (as cross domain communication isn't supported at this time).