Shrimp Aguachile with Coconut and Avocado

Name: Shrimp Aguachile with Coconut and Avocado
Ingredients: 1 whole fresh pineapple (about 28 ounces); ¾ teaspoon fine sea salt, divided; ¼ cup unsweetened coconut milk (from 1 [13.6-ounce] can, well shaken and stirred); 1 medium (1-ounce) lemongrass stalk, trimmed and roughly chopped (about 2 tablespoons); 1 tablespoon chopped peeled fresh ginger; 1 small serrano chile, halved (and seeded, if desired); ¾ cup bottled coconut water (such as Vita Coco Pure Coconut Water) (from 1 [11.1-ounce] bottle); 5 medium (2-ounce) celery stalks, divided; 12 peeled and deveined tail-on raw large shrimp (about 8 ounces); ⅔ cup fresh lemon juice (from 4 lemons), divided; 4 dried chiltepin or pequin chiles (unseeded), crushed; ¼ cup shaved coconut chips (such as Mavuno Harvest Dried Organic Coconut); 1 medium (6-ounce) avocado, quartered lengthwise and thinly sliced crosswise; ½ cup loosely packed fresh cilantro leaves; ¼ cup thinly sliced red onion (from 1 small [5-ounce] red onion); 1 small (2-ounce) Persian cucumber, thinly sliced into half-moons (about 1/2 cup); ¼ teaspoon flaky sea salt (such as Maldon); Tortilla chips, for serving (optional)