Are you really from Brisbane? If so don't forget Americans do not get any exchange rate protection as the Duham is linked to the American dollar at a fixed rate of 3.67-1.00.
Also, ASD's tuition just went up 22% and the seat fees also increased about 30% so once the little ones are in grades KG2 to grade 6 you will be out of pocket between 2200-2800 Dhs ($600-$760) per student, per month. Takes a big chunk if you have a few kids there.
...aside from that your budgeting looks sound to me. Must have a small car though with payments like that.