Is there a requirement that you have to do two breadth subjects in first year, one in each semester?
Nope, not at all. You could do none in first, two in second. Two in second, none in first. None at all for the entire year if you wanted. I, as one example, didn't do any breadths in the 1st semester of my second year, then did two breadths in my final semester in third year.
It doesn't matter how you take the subjects, only that you fulfil the requirements of your course as it is laid out in the handbook and manifested on the study plan.
The problem with going a little bit off the beaten path is that you may run into trouble with prerequisites, so make sure you've mapped out your study plan pretty well beforehand.
This may be a funny question (since I'm a Jaffy
).... but what is Chem 1 like at Melb.
You'll find a few reviews in the subject review thread.