Holy crap man.
I did Chem in year 11. You'll be fine, and you'll do really well in it, AS LONG as you revise your notes every night. Chem's one of those subjects you cant slack off in. They're all reasonably meaty subjects, and have a decent scaling, so just put your head down and you should get an awesome UAI
you will go well with any combo of subjects just as long as you work hard and do reasonably well.. there is no point doing all the harder subjects that supposedly scale well if u are going to bomb out in them.. better off doing the so called 'easier' ones and killing them