The words "necessary and proper" apply only to "powers" vested by the Constitution or among the "foregoing Powers".
The preamble to the Constitution explains WHY the Constitution was implemented but the reasons listed do not amount to vested powers. Nowhere is there a vested power which amounts to "Congress shall have the power to regulated the keeping and bearing of arms by the people". In fact, the Second Amendment says just the opposite.
The words, "Promote the general welfare", contain no limitation whatever on what might be considered by Congress to be consistent with this phrase. There would be no need for any enumeration of powers if this was what was intended by our Founders.
Yes there is a limitation. The Congress only has the enumerated Power to make laws regarding promoting and providing for the general welfare, and that is the exact reason why the Constitution was formulated. Although Congress is the font of all laws by, of, and for the general population, it is not given the Power to execute nor of justifying its laws. Those Powers are obviously distributed exclusively to the other two branches of the government. Furthermore, none of those Powers are given to the fourth estate, but the Power to criticise and howsomever communicate to the general population is.