Hi there,
I'm in Year 11 and currently doing out of your subjects: Maths (2 unit and 3 unit), Biology, Chemistry and Advanced English.
Biology from my experience is pretty straight forward. The concepts are easy to grasp and there's quite a bit of memory work involved. The content is engaging and really interesting, and the workload is decent. You will get an assignment every term though, and these may require a fair bit of work, but nothing too demanding.
Chemistry is a whole workload heavier. The concepts are more difficult to grasp and you need to UNDERSTAND what is going on at the molecular level, rather than just KNOW. So you need to do alot of extra reading, and ask lots of questions. Chemistry needs a huge amount of practice and time if you wish to get a good mark. There are calculations involved, which may get slightly difficult. If you practice and do the extra work, it won't be as hard as people make it out to be. I'm actually enjoying it. If you are really interested in learning about elements, compounds, and the chemistry behind reactions, then you should pick this. But do a significant amount of research before you pick it. Make sure it is what interests you, as this is what will motivate you to work harder and ultimately get a high mark. Talk to some students who are doing Chemistry in your school. Prepare yourself for a pretty heavy workload in Year 12, though!
Maths is ok. It just requires alot of practice, and you need to keep up to date with everything. Don't let things pile up. It's an easy enough continuation from 5.3 maths in Year 10 if you were in the A class. Ask your Maths teachers whether they believe you are capable. Usually, they know best. There is a LOT of homework involved, and you need to constantly be doing revision and practice questions. It will get more difficult and the workload will increase in Year 12. But I greatly recommend this over General Maths!!! It's not difficult if you practice!! The topics you do are: Plane geometry, functions, arithmetic and algebra, trigonometry, tangents and derivatives.
English is not too bad. It helps if you have an interest in it. There's a lot of Shakespeare and analysis and essays. It requires a deeper level of analysis. Not too difficult if you keep practicing essay writing. Definitely pick this over Standard... Standard is a trap!
Go to a book store and flick through some HSC and Prelim textbooks. Read through them. If you feel that you may have an interest in these subjects, then go ahead. If you can organise yourself, you'll be fine. Do lots of research about the subjects and ask teachers and students at your school. BEST OF LUCK!! Do what you WANT to do