Preheat oven to 450 degrees F.
Make chile cascabel tomato salsa roja. Place tomatoes and garlic cloves on a sheet pan and roast in the oven for 15 minutes or until charred, rotating halfway through. Remove from oven and set aside.
Remove stems and seeds from cascabel chilies and chile de arbol. Heat a pan over high heat and toast chilies until lightly charred, about 2-3 minutes. Remove from heat and transfer chilies to a pot. Cover with water and bring to a boil over high heat. Turn off the flames, cover the pot, and let sit for 10 minutes.
Remove chilies from water and transfer to a blender along with roasted tomatoes, roasted garlic, and ¼ cup water. Blend until smooth and season generously with salt and pepper. Let cool completely.
Make lime crema. Combine sour cream with lime zest and juice, and garlic. Season with salt and pepper and set aside.
Prepare the seafood. Make an ice bath by combining cold water and ice cubes in a large bowl. Set aside.
Combine 5 cups of water with red wine vinegar in a large pot. Squeeze lemon and add the lemon to the pot along with sliced red onion, chile de arbol, garlic, rosemary, bay leaf, and salt. Bring to a simmer over medium heat. Add shrimp and scallop and cook for 2-3 minutes or until pink and firm. Immediately remove the seafood from the broth with a slotted spoon and transfer to the ice bath.
When cool, remove the seafood from the ice bath and chop into bite-size pieces. Season with salt and pepper and add 2 cups of the salsa, tossing to coat. Add more salsa if needed.
Assemble the tostadas. Spread lime crema on the tostada shells and top with the seafood, cherry tomatoes, avocado, sliced radish, and pickled onions. Serve immediately with lime wedges and extra salsa on the side.