To make crema: In second bowl, whisk sour cream and 2 tablespoons lime juice together, and season with salt and pepper to taste. Set aside.
To roast chorizo and corn: Combine oil, chorizo and corn in bowl. Remove sheet from oven and spread chorizo and corn in single layer on hot sheet. Cook until browned, about 15 minutes.
To prepare beans: Meanwhile, drain and rinse beans. Combine broth, chopped jalapeños, remaining 1 tablespoon brine and beans in clean bowl and microwave until warm, about 2 minutes. Mash beans with potato masher or fork until spreadable, season with salt and pepper to taste, and spread evenly over tostadas. Arrange on clean rimmed baking sheet, overlapping tostadas as needed.
To finish: During final 5 minutes of roasting chorizo, transfer sheet with tostadas to lower oven rack to warm through. Remove tostadas from oven. Transfer chorizo-corn mixture to large bowl, and stir in remaining 1 tablespoon lime juice and the tomatoes. Divide mixture evenly among tostadas. Top tostadas with slaw and crema. Crumble cheese over top and sprinkle with cilantro.