Melbourne is decent for physics. To be honest, I'd try and stay away from Monash - its physics department isn't amazing (unless you really want to go for the engineering side of things), and it's not well known for pure maths. It's amazing for chemistry though, if that piques your interest. I can definitely say that maths and physics at Monash do NOT seem to be as rigorous as maths and physics at ANU and Melbourne. I did UMEP physics at Melbourne, and a semester in the PhB program at ANU (feel free to message me about it), and the courses were much stronger and much more proof oriented than what I heard about the courses at Monash. Sydney is also well known for physics. UNSW and Monash are more engineering-y.
The BSc students at ANU take exactly the same classes as the PhB and Advanced Science students, but don't have as many opportunities to do research. If you get good grades in the BSc or the BSc (Advanced), you can transfer into PhB. If you've got substantial accomplishments in science (olympiad awards, either at international or national levels), they might waive the cut off slightly (my friend who got just below 98 with an IChO medal is doing PhB).
Career options for physics include research, academia, defence force sort of stuff, further study (engineering, law) and finance. Apparently physics majors are loved by financial firms in the US. Mathematicians can work in finance, financial engineering, logistics, research, any form of mathematical modelling... there's also a lot of options.