Question

k

Answer 1

Do you want one quote or a quote for each?
The conclusion covers all three. (That's the last paragraph before the signatures.)

Answer 2

popular sovereignty:
We, therefore, the Representatives of the united States of America, in General Congress, Assembled, appealing to the Supreme Judge of the world for the rectitude of our intentions, do, in the Name, and by Authority of the good People of these Colonies, solemnly publish and declare, That these united Colonies are, and of Right ought to be Free and Independent States;
or just:
in the Name, and by Authority of the good People of these Colonies,

Answer 3

natural rights:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.

Answer 4

social contract:
That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed,