As I posted earlier to visit a rural supplier store and get some advice. I did when I started on my plantation 14 years ago as a complete novice. There are herbicides that kill weeds and not pasture. There are premergance sprays that kill seeds before they germinate. Each State (area) has it's own problems and therefore own solutions. What works in Northern NSW may not be suitable for your block but the local Ag store guys will know what will and save you a lot of time and effort to get you block looking like you want it.

Whitewood