Step 1Cook celery, carrots, onion and 2 cloves minced garlic in 3 tablespoons olive oil in large soup pot over medium-high heat until softened, about 10 minutes. Add 1 cup white wine and cook until reduced by one-third, 5 minutes. Add tomatoes and turn heat to low.
Step 2In large covered skillet, cook clams with remaining white wine over high heat 3 minutes. Add mussels and cook, shaking occasionally to keep from scorching, until all shellfish are opened, about 5 more minutes. Remove shellfish from pan, cover tightly and refrigerate. Strain remaining liquid into measuring cup and add enough water to make 4 cups.
Step 3Peel shrimp, reserving heads and shells. Place shrimp meat in plastic food bag, seal tightly and refrigerate until needed. Add shrimp shells and cooking liquid-water combination to soup pot and cook over medium heat 25 minutes.
Step 4When done, ladle contents of soup pot into food processor and grind 5 minutes. Press through strainer into bowl. This may need to be done in batches. Add saffron to strained broth, cover tightly and refrigerate.
Step 5Cut oily and white fish in chunks, place in plastic food bag with 1 clove minced garlic, salt to taste, crushed red pepper flakes and 1 tablespoon olive oil. Seal tightly and massage through bag to evenly distribute ingredients. Refrigerate.
Step 6When almost ready to serve, bring broth to simmer, add oily fish and white fish and cook 5 minutes. Add shrimp and cook until firm all the way through, about 5 minutes more. Add reserved clams and mussels and heat through. Season to taste with salt.
Step 7Toast baguette slices and drizzle lightly with olive oil. Arrange baguette slices in wide soup bowls and ladle fish soup over top. Serve immediately.