Why is Tris’s government run only by members of Abnegation? Do you think this is a good idea? Do you agree with her father’s statement that “valuing knowledge above all else results in a lust for power, and that leads men into dark and empty places?

No, no government should be led by the people of one group or in this case faction. Balance is necessary, character traits are diverse, and all types of people and talents are necessary in creating a balance. Selflessness is an integral trait in any leader, but Abegnation also tends to deny or reject what they cannot understand. As for Tris' father's statement, I completely agree. Absolute power leads to corruption, this has been proven incessantly throughout history.