I did my HSC in 2015 and got a band 6 in Legal Studies, English Advanced and SOR 1U, so speaking from experience,
SOR 1U and Legal Studies are great subjects that are relatively easy to get a band 6 in, and also don't require much work if you have a good teacher and/ or tutor, particularly in legal studies where you need to keep up to date in your cases, media, legislation. If this isn't the case, you will find you may struggle in legal as it will take up a lot of your time!
As for adv English and Ex 1 and 2U Math, these scale well so yes, definitely possible to get an above 90 atar with these.
I don't know much about Senior science but, business studies doesn't scale comparatively well to the other subjects.
In terms of dropping, I would recommend getting rid of senior science or business studies. However, if you are not comfortable going into your HSC with 10 units, and want a 'back up unit' in case you mess one up, then I would drop SOR 1U or ex English.
In terms of scaling, once you hit a mark of 90+ in EVERY subject, subjects don't scale down, except for minor discrepancies. If you want to test the scaling of your subjects yourself, I recommend you go onto the 'Matrix ATAR calculator' website...one of the most accurate and set the same mark (try one under 90) for all your subjects as this will show you which subjects scale up/ down.
If you want to excel in all your subjects you need to be willing to put in the hard work. Your teachers should provide you a comprehensive set of notes for all your subjects so it is up to you to use those resources to complete as many practice papers as you can get your hands on, particularly for maths! For english & legal (in particular when you get to the HSC for legal), make sure your thesis statements are blendable to a wide range of questions. If you find your teachers aren't teaching you to the best standard, I would look into private tuition which can really help, particularly if you find a tutor who provides detailed notes and can help you master the nuances of the course.
This isn't so important in year 11, but when you get to the HSC, make sure you ANALYSE your English texts yourself! This will set you apart from the rest of the students sitting the advanced/ ext course in your school as you will have different analysis to that of your teachers!
If you find yourself looking for a tutor, I have been tutoring English Advanced and Legal Studies to year 11 and HSC students for the past year, my current HSC students of which are performing exceptionally well, so feel free to send me a message!