#1) I think it means that when a government tries to have too much control of over a group of peoples then there will be sedition to that control. The best government is one that lets people freely choose the way they live.
#2) Justice may or may not be amidst a majority, but in most cases the majority manifestly falls into justice. People (at least in the open) want to have justice because it relates to a standard of morals and ethics. A conscience no matter the origin wants justice in their life (at some level depending on the person), but a conscience may be lead in the wrong direction. For example, I am reading Huck Finn in one of my classes, and in this adventure Huck is accompanied by Jim, the runaway slave. They float down the river in a raft and they form this ghastly friendship that is unknown to the late 1800 century peoples. Huck has been taught all his life to show no humanity towards slaves, but as this relationship develops he sees that they are in fact human and this way of thinking is wrong. This example shows that a conscience can be lead the wrong way and indeed think to be right but still at the same time showing no justice. A conscience may feel incompatible with the majority. He or she may be right, but they need to question and think about the situation seeing the more just choice.
In the #2 marked section a majority may however make a choice based on what they want or their conscience causing an injustice. " a corporation with a group of conscientious men is a corporation with a conscience." I interpret that this becomes the conscience that makes the choices. All three, majority, justice, and conscience, are intimately intertwined; one affecting the other affecting the other.
#3) Differentiation is imperative in order to have successful results. For example, it is like having the wrong cable in the wrong port in a computer. You want your printer to work compared with you want a law changed.