On a small flat plate, stir together 3 tablespoons salt and the lime rind; set aside. Pour 1/4 cup of the lime juice into a shallow bowl and set aside. In a blender, combine cucumber, avocado, tomatillos, grapes, cilantro, Serrano pepper, remaining 1/4 cup lime juice, celery salt, 1/2 teaspoon kosher salt, the hot sauce and black pepper; whirl until smooth; mixture will be slightly thick. Transfer to a 2-quart pitcher; stir in coconut water.
Add tequila or vodka to taste, if desired. To serve, dip glass rim in reserved lime juice, then into salt and lime rind mixture. Add ice and fill with “Guaca Mary”. Thread avocado, grape tomatoes and pickled onions onto toothpick or skewer for garnish, if desired.