The Quantity Theory of Money is not an Austrian concept, and its not an axiom. Its really trivial because its true by definition.
The second statement here follows from the first so only the first is an axiom.
I think what you’re asking relates to this:
Economics, and here Rothbard follows Ludwig von Mises, sets out from the axiom that humans act, i.e., that they pursue their most highly valued goals with scarce means. Combined with a few empirical, and empirically testable assumptions (such as that labor implies disutility), all of economic theory can be logically deduced from this indisputable starting point. (Source)
So the question is, what are these “few empirical assumptions”?
- Labor implies disutility.
- ?