If you were to take Business Studies, you probably would not find it difficult. Its essential purpose (this applies mostly to the Preliminary course) is to introduce you to the different aspects of the business world. It does so through three topics, the first being an introductory one covering the nature of business and the other two exploring business management and business planning.
The HSC course builds on the foundation of knowledge that you gain as you complete the Preliminary course. HSC Business Studies is more specific and emphasises four key business functions, being operations, marketing, finance and human resources. In addition to the content, you will also study and incorporate real life and/or hypothetical business case study material into your responses, mainly Section IV responses.
Compared to Economics, you are likely to find Business Studies easier. Given the nature of Economics as a subject that explores only one area of business in more detail than Business Studies, which explores a multitude of business fields in slightly less detail. With that being said, you can definitely expect both subjects to be content-rich, meaning that it is important to ensure that you are up-to-date with the content and the syllabus. Coupled with sufficient practice (i.e by completing relevant practice material), favourable performance will hopefully be within reach.
I hope this helps!