Rinse the dried ikan bilis with cold water and place it in a pot. Pour in the 5 cups of water and bring to a boil. Turn down the heat and cover the pot with a lid. Simmer, covered, for 20 to 30 minutes. Strain the stock and discard the ikan bilis. Set the stock aside.
Place the potato noodles in a large bowl and add in enough water to cover the noodles (I used tap water at room temperature). Set aside for at least 30 minutes until softened. Drain and set the noodles aside.
Heat oil in a large frying pan or a large pot over medium heat. Add in the onion and sauté until translucent. Add in the garlic and sauté until fragrant. Add in the mushrooms and sauté until the mushrooms have browned and shrunk in size. Add in the kimchi and stir-fry for several minutes.
Add in the kimchi juices (if any), 3 1/2 cups of stock and gochujang. Bring to a boil and simmer for 15 minutes.
Add in the drained potato noodles and pork slices and stir them in. Arrange the tofu on top and simmer for 5 minutes until the pork is cooked and the tofu is heated through. Add in more stock if needed and drizzle in the sesame oil. Arrange the radish sprouts on top and serve with rice.