On a typical night, the crowd on the main beach area for fireworks viewing is not going to be particularly large. Yes, there will be plenty of people around - but it's not overwhelming in my opinion.
Everyone likes to crowd in a little sliver of beach the provides a view corridor between the end bungalow and an island in the middle of the lagoon as that's the most direct area with the castle in view. The zone is roughly between the yellow lines below. If you get to the left of this zone, the island blocks your direct view of the castle (just barely) but you can still see plenty of fireworks. The audio is actually better the closer you get to the boat dock, so it's not a bad spot.
But the beach area is plenty big and easy enough to move around if you don't like your view, the audio, or crowds on your night. Hope you enjoy your trip.
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