Warm tortillas, without crowding, in a single layer on a medium-hot griddle or in a 10- to 12-inch frying pan over medium-high heat, turning once, until hot and flexible, 30 to 60 seconds per tortilla. As they're heated, stack in a basket lined with a thick towel (or in an insulated tortilla warmer); add more tortillas to griddle. Or divide tortillas into 3 equal stacks, seal each stack in foil, and heat in a 350° oven until hot in the center, 12 to 15 minutes; unwrap and stack in a towel-lined basket.
Place fillings, salsas, sauces, condiments, vegetables, and beans in separate containers and arrange on buffet (see notes); keep those that need to be warm on an electric warming tray or over a candle (stir occasionally to prevent scorching).
To assemble each taco, stack 2 tortillas on a plate and spoon filling down the center; add salsas, sauces, condiments, and vegetables to taste, and fold tortillas over filling to enclose. If desired, wrap with a napkin, and hold to eat.
Condiments and vegetables: 2 cups total (about 10 oz.) crumbled cotija cheese and/or shredded white or yellow cheddar cheese or jack cheese; 1 1/2 cups Mexican crema, jocoque, or sour cream; 6 cups total shredded iceberg lettuce, a mix of romaine lettuce and red cabbage, or green and red cabbage; 1 1/2 cups chopped onions (taquerias typically use those with white skins); 1 cup minced fresh cilantro; 2 cups diced firm-ripe tomatoes; 2 firm-ripe avocados (1 lb. total), peeled and coarsely mashed with 2 tablespoons lime juice; and 3 limes (3/4 lb. total), rinsed and each cut into 6 wedges.
Nutritional analysis per 2 corn tortillas.