Hey!
I reckon it's perfectly doable.
Have you watched the ATARNotes Major Works Crash Course lecture by Lily during the July lecture series? She did 4 majors including Ext 2 English and History Extension and still did well for her HSC!
Another well-known example I can think of is Gladys Lai from the Class of 2016. She did 4 units of English, 5 units of History (Ancient, Modern, and Extension) alongside Visual Arts (which also requires a major body of work!) and achieved a perfect 99.95 ATAR along with 5 state ranks.