You don't need case studies for the SDME, but it may help with your background knowledge. For the 16 marker, my teacher recommends you constantly link back to:
-Place name (That way you make sure you are answering relevant points and staying on track)
-Social, Economic, Environmental
-The Resources: Use data from the resources and actually mention in your answer what resource you have referred to (..as shown in resource 3..)
I think the last SDME on Rivers & Coasts was on Rivers so hopefully this time it will be coasts!