1: One could argue that the purpose of regulating commerce has the end intent of promoting commerce. However, it depends on what actions are taken to "promote" commerce. Regulations that assure ease of transportation, smoothing any conflict between state regulations on certain types of products, etc. are most assuredly the eenumerated perview of Congress, all of which, if done correctly, would have the net effect of promoting commerce.
However, handing out tax breaks, grants, etc. to preferred corporations is NOT a valid extension of regulating commerce.
2. No. That authority was reserved to the states. The general welfare clause that is often pointed at in article 1, section 8 refers to the general welfare of the United States - that is, the union as a whole. This is a necessary and important, though often misunderstood and misused distinction. The Constitution is very consistent in that when the writers mean the people of the United States, they say "the people"; when it is the individual states they use "the states" and when they mean the nation as a whole, the say "The United States.
3. The Constitution itself is the end result of the individual and collective intent of the people who wrote it, promoted it, and exercised its ratification. Every individual's intent is involved. There were three main focuses in writing this Constitution. The first was to replace the central government of the Articles of Confederation, which were not working, with a stronger federal government. The second focus was to assure the authority of the individual states was not usurped by the new federal government. And the third, led by the anti-federalists, was to assure federal authority could not be used to usurp individual liberty. The result is a collective effort of these men and their ideals. No one ideal or original intent holds sway above the others because the resulting document, the Constitution itself, holds the compromises worked out between the varying philosophies.
There was a general agreement, even among the more staunch federalists such as George Washington, that the overall purpose of the Constitution was to define the role of the federal government. They understood the need to define it, so that it could not grow, without the consent of the people, beyond its defined powers. Nowhere will you find any of the writers, delegates, state legislatures that enabled it ratification, etc. support for the idea that the federal government has the authority to interpret its own limits. Anyone with that ideal would have fought against the Constitution since it's very nature is to define and limit governmental authority. That is why the original, unamended constitution is filled with those things government is forbidden to do. Then, to make certain it was understood that what the constitution says government can do is ALL the government can do, they added the 10th Amendment.
