Looking at your current units, you should probably prioritise English Adv, Maths Ext 1, Maths Adv, English Ext 1, English Ext 2, Chinese and Drama/Entertainment in that order.
English Adv ->Always counted in your HSC
Maths Ext 1 + Maths Adv -> Very high scaling + easy as you have mentioned you...
Also if possible, could you provide school averages?
You may find them if you search up "[your school] HSC annual report" but if you can't its alright.
Don't stress too much on prelim marks unless you're aiming for extension 2 subjects. Also, marks themselves don't matter, you should care more about your relative performance compared to the cohort.
For short answer questions, you can use trial papers or HSC papers.
Essay questions are a bit trickier but I tend to find exemplar essays for the text and understand what makes them good. Also knowing the rubric/syllabus very well is important as well. Not sure how applicable this is for Y10...