AussieHunter,
Alan Mckenzie has pretty well covered it in answer to your questions.
I don't know whether there would be any scrub bulls in your area but there could be wild cattle which have wandered off from the mob.
Most scrub bulls that are found across the top of Australia, in Cape York, The Territory, and West Aussie have never been branded or yarded and have mainly come from wild stock.
They are often quite easily hunted and killed but they can also be very dangerous animals.
They can be cunning, fast and as agile as a cat.
Bulls that have been chased by choppers, 4x4's, motorbikes and horses during muster, and have escaped, can have a nasty disposition. Same goes for bulls that have been harassed by pigdogs.
If you ever get caught in open ground with an angry bull you are in a lot of trouble, and this applies not just for wild bulls, but for some farm bulls as well.
If a bull reaches you on open ground, you're stuffed.
Shooting undisturbed bulls with scoped rifles at some distance is really not much of a challenge.
The best way is to get up as close as you can on foot, let the animal take a real good look at you, and then take him with a big open sighted rifle, preferably a double!

Even if you don't find in bulls in your area I'm sure you'll have a lot of fun hunting for them and no doubt there will be a few boars around to make the time spent looking worthwile.
Best of luck.