It's hard to define how hard it is to get a certain ATAR because there are many factors that determine that such as:
- how smart the individual is
- How much work they are wiling to put in
- How effective their study is
Don't worry too much about an ATAR for now. Just focus on doing well in your subjects and understanding the content, particularly for subjects you want to do later like maths advanced or extension, you need to have a solid base understanding of previous years maths. English is sort of similar but still even if you don't do amazing in year 10 you can definitely improve in the two years of year 11 and year 12.
Try to instead obtain good study habits, note taking and studying methods etc.
Just a personal input into this don't limit yourself as to what you think u will get for the ATAR. At the start of year 10 was probably looking at around a 94-95 based off my ranks. But then that estimate increased in year 11 to around 97-98 as my ranks improved and further increased in year 12 to what I got (in signature). The main reason I would say it increased is because my work ethic improved and I was able to find what study approaches worked for me and what didn't. Which you can only learn if you try different things earlier on