well roughly about that yeah. 4 units means 4/10 units of your ATAR so yes you should be putting in roughly half your time into 2/3/4U maths. Don't neglect your other subjects either
not at all. The HSC course is watered down to suit everyone; not just the ones with superior mathematical backgrounds
I didn't do HSC engo studies and aside from the fact I failed PHYS1A, I am doing quite well at uni