This link is to the Disney website map of the park. Enlarge the map so you have a view of the walkways around the castle.
For park opening in the morning with the main castle walkway closed, go to the left and into FL that way. It's going to be very crowded on that path as so many people are doing the same thing as you are. Watch out so you don't get run over with a stroller or scooter.
You'll see there is a path on the right side too but I believe it's closed for refurbishment to Snow Whites grotto area and wishing well.