You are correct, Gates E51-E76. I didn't even know it was called La Galerie Parisienne, I'm just new in town
I believe you won't be able to go to E51-E76 unless you have a connecting flight out of those gates. What they call "Customs" at CDG is just a bunch of counters on the exit from the luggage claim area, which sometimes you won't even notice, as you just walk through without having to talk to an agent.