Does this mean that all four of the above are "equipotent"?
No. The inclusion of these foundational documents in the Front Matter of the United States Code does not indicate anything regarding their legal status. It is more of a political statement, as a preamble to all laws in today's sovereign federal state, describing the foundation of the United States of America and its constitutional order.
The only constitutional law in force today in the U.S. is the Constitution for the United States of America, beginning with
We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.
and the subsequent amendments.
The ratification of the Constitution replaced any previous constitutional orders in effect between the States. A new government was created by the Constitution and replaced the old one under the Articles of the Confederation:
Both Governments could not be understood to exist at the same time. The New Government did not commence until the old Government expired. It is apparent that the government did not commence on the Constitution being ratified by the ninth State; for these ratifications were to be reported to Congress, whose continuing existence was recognized by the Convention, and who were requested to continue to exercise their powers for the purpose of bringing the new Government into operation. In fact, Congress did continue to act as a Government until it dissolved on the 1st of November, by the successive disappearance of its Members. It existed potentially until the 2d of March, the day proceeding that on which the Members of the new Congress were directed to assemble.
Owings v. Speed
The States abandoned their old agreement (the Articles of Confederation) and subjected themselves to the new Constitution.
Of course, the other documents remain historically very significant and may shine lights on the interpretation of the present Constitution, for example, in Texas v. White, the reference made to the concept of "perpetual union" found in the Articles.
The Declaration of Independence is not so much a legal document per se but a declaration of the existence of the States sovereign from the British Crown; but such sovereignty is not a result from the declaration, but from the acts of war.
The Northwest Ordinance of 1787, while remaining in effect under the Constitution by Acts of (the new) Congress, is in any case spent as its territorial extent is extinguished by the establishment and admission of states, who enjoy equal status under the Constitution. See for example, Permoli v. Municipality No. 1 of the City of New Orleans and Strader v. Graham.