I think it is best to know all
2016 HSC paper has a MC question on all acts - you would not know the answer unless you know each act in detail and its responsibility.
2017 HSC paper in short answer section asks you about consumer laws - notice how they say laws not law - meaning different types - so five distinct points. Also, the syllabus above shows the 4 main heading under consumer laws which you would use to answer the question.