I have the same textbook, and I already know the answers.
(1) Archeological Sources are the main sources for studying the Harappan Civilization because the Harappan Script has not been deciphered yet. It is also because our knowledge about them is Scarce.
(2) Yes. The Harappans cities were well planned, streets cut at right angles, public buildings like granaries were in plenty and well kept drainage-sewage system and so on directly points to the Engineering skills of the Harappans.