I recently started working with Adobe Edge, and need to create an additional stage for a more complex animation. How can this be done?
There's only one stage per document with Edge, just as with Flash or AE. You can build animations as symbols with their own timelines inside the stage, though, just as you can with Flash movieclips. That should get you where you need to go.
This video by Mark Anders covers symbols, starting about 5m 10s.