I paddled the marsh this morning. It took me approximately one hour to paddle from a bridge crossing through the marsh to Goul's Inlet and then south along the coast line to the Coast Guard Station (major public beach access).
The paddle was easy and quiet since I was following the tide out at 7am. There are no real tricks to the river. When it empties into the ocean you can go straight across to Sea Island for some beach combing. Or you can head to the right along the St Simons coast.
public restrooms at Coast Guard station/beach parking.
from the St Simons Island causeway go straight through the main driving circle. Then follow the road to the big public beach access. You will turn left towards the beach and cross a small causeway. When you see a bridge pull over and unload your kayak/boat. Then continue another 200 yards to the beach parking. This is the only real parking that is close by.
You could also drop a bike off at the east beach access, which is where the inlet is (makes for a shorter trip) and then have about a 40 minute trip. It's not too hard, locals can always give you directions.