Finely chop enough lemongrassstalks to measure 4 teaspoons. Cut remaining stalks in half. Place beef and stalks in large pot. Add broth and 8 cups water; bring to boil. Reduce heat; simmer 1 1/2 hours.
Heat oil in medium skillet over medium heat. Add 1/3 of sliced onions and garlic; sauté 1 minute. Add 1 tablespoon sambal oelek, paprika, and chopped lemongrass; sauté 1 minute. Add sambal oelek mixture to soup; mix in fish sauce, sugar, shrimp paste, and salt. Simmer until beef is tender, skimming foam from surface, about 1 hour. Remove beef from soup. Skim fat from surface of soup. Simmer soup until reduced to 8 cups, about 10 minutes. Add more sambal oelek for spicier flavor. Trim off any fat from beef; cut meat into bite-size pieces.
Bring large saucepan of water toboil. Add noodles; boil 1 minute. Drain; rinse under cold water and drain again. Using scissors, cut noodles crosswise. Divide noodles among 4 large bowls. Top with beef, remaining sliced onions, green onions, and cilantro.
Bring soup to boil; ladle over noodles. Toss cabbage and rau ram in small bowl. Sprinkle over soup. Top with chiles, if desired; squeeze lime over.