Hey LivRose!
Welcome to the forums
ATARs are a ranking that compare your performance to the other QLD students in the same year. The higher your ATAR, the more courses you'll be likely to get into. Only your unit 3&4 studies contribute to your ATAR calculation.
One difference between ATAR and OP is that ATARs are a
lot more specific. ATARs go up to 99.95 in 0.5 degree increments (ie you could get 99.95 (highest possible), 99.90, 99.85, 99.80...). I find that the easiest way to think about the ATAR is as the percentage of the state you "beat" (Eg. To get a 70.00 ATAR you scored higher overall than 70% of students and are in the top 30% of Queensland students for that year).
Definitely can't guarantee anything, but based on preformance patterns in other states you can probably expect most of your subjects to scale up, especially specialist maths.
The workload will get worse but your coping skills & methods of managing this are likely to get better too. Going into year 11 is a significant step & it makes sense that you'll take some time to adjust.
With the high amount of things taking time your time it's very important that you make sure you have time to take care of your health. Sleep deprivation, lack of exercise etc. can really contribute to stress and difficulty balancing everything. It might seem counter-intuitive, but there's a point when studying too much and neglecting your health damages your learning.
Of course, you might be managing having a lot of commitments better than I did and already taking good care of your health - but if you're not it's very helpful to change that.
In terms of studying and assignments, I found practice questions & teaching others to be the most effective ways for me to learn. Teaching others was other students at my school, people on atarnotes (making notes to share, answering questions etc) and some other students too.
Let me know this makes sense and if you have any questions