There are two ways and please follow the extending BRS Guide and Configuration Guide.
Please follow the extending BRS guide and configuration guide.
Yes, you can easily do. A rule service is similar to an axis2 service. You can configure QoS for a rule service through service management admin UI or manually editing services.xml of a rule service
Yes, Rule component has been integrated to the WSO2 ESB as a mediator. There are a set of samples demonstrating it. Please checks the rule sample guide in the WSO2 ESB documentation
If you need to take features offered by the services.xml such as setting session scope , then you have to use a services.xml.
If you have facts as a Jar file, rule set as a file, or if you require a services.xml (Axis2 Service Configuration), then, the rule service (.aar) should be used.