If you're South African, you first need to get a competency.
This will be through a certified instructor near you. Your local gun shop will be able to help.
This takes roughly 3 months. Then you purchase your rifle.
You will now need your competency and a motivation letter. You will need to show that you need the rifle, that you hunt and have proof. Letters from land owners , pictures etc. these motivations can be done for you for a fee, again chat to the local gun shop.
This should take another 3 months.
Then hopefully you can collect your firearm.
As for calibre, with the limited number of firearms you can own, I would go 243
Best of luck
Regards