i think its better to be concise and succint rather than targeting a specific word limit to begin with.
I was going to say the same thing. If your teacher says you tend to waffle, I'd go back over it to make it more succinct. Plus, if I was your teacher, I'd definitely rather read shorter concise paragraphs, than receive an essay with super long paragraphs (i.e. just a block of text).
Anyway, based on the criteria sheet, and the lack of an actual topic, it does seem that you can be quite broad, and there's a lot to write about.
One tip I have, is to make sure you mention relevant section numbers of the Constitution (e.g. mention section 128 when discussing the referendum). I'd also talk about how although Australia only has five entrenched rights (compared to however many the country you're comparing it to has, rights are protected by ordinary legislation, etc. = effectiveness of not having a bill or rights vs. having a bill of rights)