I don't think you need to start and stop the slot component programmatically. doStartService() is called internally after a service (component) has been created, placed into the Nucleus naming hierarchy and initialized with its configured property values. We generally override doStartService() method in our component class to do any additional processing that we may require when it starts. Similar concept applies to doStopService() when a component shuts down.
Using ATG Scenario, you can populate slot content using a targeter. A lot would depend that how you designed your scenario and what events you are trying to capture. For your requirement of refreshing the slot content you try making use of other slot component properties for limiting number of items in slot, event generation, item retrieval settings etc.