Personally, I think uni and the HSC are a very different kind of dificult. One or the other might suit different people better.
There's definitely less spoonfeeding, resources and past papers etc. around for uni and not all subjects work the same way as each other or are as formulaic as the HSC. I would say there is an increased emphasis on you being able to manage your own time and guage what certain subjects and assessments expect. Going to all the classes and doing all of the work puts you in a good position but, unlike school, that's generally on you.
If you're interested in Law/Business, go for it. Business is generally considered on the lower end of the scale in terms of dificulty and Law the harder side. But from my understanding one of the dificult parts of law is the sheer volume readings you have to do and reference in your work.
