More than 400 pages of legislation detail the duties and powers of the Consumer Financial Protection Bureau that Congress is set to create. But the first director of the powerful new agency will play a critical role in determining how it works. “Whoever is in command will determine the agency’s path,” said Kathleen Engel, a Suffolk University law professor who sits on the Federal Reserve’s Consumer Advisory Council. “When you have a lot of power vested in an agency, everything depends on how effectively they carry out their rulemaking authority.”