Whoops - totally missed that you were doing Software Development already, haha!
It's a shame that your school is forcing you to do 5, but maybe that extra increment you get to your ATAR will make the difference in the end, so it's certainly worth finding a decent 5th subject for next year just in case. Out of the ones you've mentioned, most have new study designs currently or for next year, meaning that most students will be flying blind, even if they have done 1&2.
Geography: FallingStar has put together a great overview of Geo resources
here, so have a look through some of those to see if this subject seems interesting to you. The
exam seems pretty straightforward as it's all short-answer questions with no major 'essay'/10-mark question component, through these questions do still require lots of evaluation and analysis, so can't escape the writing element here
Legal Studies: this subject requires more writing than the others, as you can see from the
exam, though if the subject matter is interesting to you, you might be able to look past this.
Economics: this is a slightly maths-y subject, but the advantage is that the
exam is made up of multiple choice questions too, so you won't have to worry about written responses as much. This does seem to be the most complex of the three, but again, if it's interesting to you, it's definitely worth considering.
I haven't done any of these subjects myself, so hopefully someone else can offer some more specific advice if you need it
