Essentially, past HSC exam papers offer a more accurate indication of the difficulty and the type of questions that your HSC exam will include. Based on this, you should prioritise past HSC papers. Of course, this does not mean that you cannot still attempt past trial papers, especially those that contain more difficult questions, although you should ensure that you complete enough HSC past papers. There will also be a
BoS Business Studies trial paper this year (for the first time ever), which is a resource that you may be interested in.
Generally speaking, the more past papers you can complete, the better. However, the specific number of past papers to complete is not as important as the learning and progress achieved in terms of your preparations for your HSC exam (which includes addressing areas of improvement). For example, you may attempt 5 HSC past papers, but find that you were not able to benefit much from this practice as you may still have areas of improvement that you were not able to address. On the other hand, you may complete 3 HSC past papers and benefit more since you might have been able to address particular issues that you were facing, despite the lower number of past papers completed.
In terms of studying in these last couple of weeks, you should regularly revise the syllabus and review the content in case there are aspects that you are not fully confident with. You should also ensure that you are familiar with your case study material and that you have a good ability to provide hypothetical case study information if needed. Other than that, you should keep completing past papers, allowing you to apply your knowledge to exam questions, and (if possible) seek feedback regarding your responses from your teacher and implement any suggestions that they offer.
I hope this helps!