Well, for both primary and secondary you need an ATAR of 70.
If you get the 10 bonus points for anything (living in GWS, academic, hardship whatever) the minimum you would need is an ATAR of 60.
There is probably a bit of room to move with this, (ie. 58 plus 10 bonus points) because the courses usually aren't full.
So if you get bonuses, 60. I really wouldn't go any lower than that tbh just because it's less likely the lower you are below 70. If you were looking without bonuses, i'd say no less than 65. Even then, probably stretching it.