Welcome to the Zone from another Aussie. I probably can't be that much help as a self taught machinist who has spent the last 12 months building his own CNC plasma machine. I have never used it but I think Fusion 360 is a good choice as it includes a CAM package and its free for non commercial use. Other (expensive) options are Inventor and Solidworks. Another might be Onshape which is cloud based.
I'd like to have a go with a retrofit using LInuxCNC but I don't have the room and Sydney is a bit to far from Brisbane!