On the CX career section it says you must "Have completed secondary school and have good passes in mathematics and science, or have a degree or diploma, or have passes in all ATPL subjects".
Now, it doesn't specifically state you need physics, but as you can understand, physics is the most relevant science subject to flying. It also says "or a degree or diploma", so if you have a diploma after you finish high school, it would seem you meet one of the education criteria. Now i'm only interpreting what is stated on the website, and it would be best for you to actually discuss this requirement with flight crew recruitment personnel to get a solid answer.
As for a salary and lifestyle on a SO salary, the current package is just under $50,000 HKD per month, this already includes housing allowance in the amount. Now whether you can make a comfortable living off this depends on what your definition of comfortable means. It also depends on where you come from and if you need to support a family or not. HK people will definitely find it easier than someone who comes from the US or Australia for example where they are used to getting more space for similar money. You're still young, so still have plenty of time to do more research and decide if its for you or not.
Goodluck.