Also how many band 6s would I need?
A 99 ATAR would require all band 6's.
Achieving a 99 ATAR is no easy feat. Once you get into that territory, it's no longer about just grinding. You need to be very, very smart with your time. Even the most organised, hard working students will end up with a 97-98, because they don't fully understand how to maximise their time. You really have to figure this one out for yourself. You're at the perfect time to do this aswell.
I'll give you an example of something i do. I always stay ahead of my maths class, both Adv and Ext. I make my notes prior to class, and complete all the exercises. This is so I can sit in class and do past papers upon past papers, and challenging worksheets. I'm then able to nit pick what i hear from my teacher in terms of picking up skilful techniques or handy tips for approaching questions. This is works for
me, and may not for you, so really configure your time strategically.
If you're at a school ranked 300th, i would hands down say being 1st in all your subjects is vital. I don't know of many schools at that rank that achieve more than 0-3 band 6's per subject. But what you also have to realise is your positioning comparative to the state. Your exams (may) be much easier than other schools. So, to better prepare yourself for your external examination, do other schools past papers - get used to the difficulty.
And of course, this goes without saying, work hard. Unless you're naturally intelligent, unfortunately theres no way around it. You're competing against an odd 70,000 student, and they won't let you have it easily.
Also I'd advise you to pick your battles. For example, Mathematics has always been my strong suit - and my school gets quite a lot of band 6's in it, and i know i'll be able to rank close to the top/ the top without putting in too much work. This allows me to focus on a subject like English which requires copious amounts of effort to top, let alone rank highly, when theres always some gunner who's been writing essays since Year 2. So, identify your strengths, and play to them.
Only idiots spread their time evenly across subjects.