Great strategy - We did this exact thing last with (with the exception of the dessert).
Perfect location at the bridge. Talked w/a CM who was directing traffic for a conference group who was slowing trickling in. She said she leaves just before the lights dim and we could fill in anywhere else once she leaves - just not where the group was sitting.
We hung back a bit and a few minutes into the show, DS & DD got to move right up to the edge of the bridge for front row viewing.
I love their expressions in the light of the fireworks!!