Iv'e heard that what you do in 5.3 maths in year 10 is the entire Mathematics course up to term 3, so if you can do well in year 10 you could probably manage Mathematics. As for extension 1, I wouldn't do it unless a) you really need it or b) you're really good at it and it could possibly make...
Well if you like english and think you'll do well go for it, but beware that you'll have to put in quite a bit of effort, especially if you want a high ATAR (which you will definitely need if you want to get into medicine). So you can't really afford to do any subjects which you doubt you could...
I remember it this way;
Spatial dimension: where things are and why they are found there, i.e. where it is occurring and what are the reasons for it being an issue there
Ecological dimension: how humans interact with their environment and impact on it
Why don't you just sit down and think about the subjects you 'really need' for your future and the university course you want.
Doing courses you a good at will probably increase your ATAR but I would drop the courses you don't need and really focus on the courses I do need to make sure I...