There is an abundance of Business Studies past HSC exam papers (9 papers from 2012 to 2020). Your main goal as part of your preparations for your Business Studies HSC exam is to complete as many papers that fall within the current syllabus as possible. Those are the papers that directly target the current syllabus and effectively prepare you for your HSC exam, provided you are constantly identifying areas of improvement (if applicable) and rectifying those as you start completing the next paper. If you somehow manage to complete 9 and still wish to attempt HSC past papers, you may carefully attempt some papers from the old syllabus, implying the need to only attempt questions that would be relevant to the current syllabus. However, if you manage to complete all 9 past papers, I would suggest attempting trial papers instead of old syllabus papers as the former also target the current syllabus, meaning they constitute more effective preparation when compared to old syllabus papers.
Similarly, for Economics, I believe your main goal should be to ensure that you are benefiting from each past HSC exam paper that you're attempting first. Once you are able to learn and enhance your knowledge of Economics content following the completion of each paper, that's when the number of papers you attempt becomes more important. There is no point in completing a multitude of papers if you're not consistently learning and addressing areas where improvement is necessary. Ideally, you should complete as many papers as possible to boost your preparations for your Economics HSC exam, so I don't think there would be a specific number of papers to aim for.
I hope this helps!