Contact Sydney thai consulate as soon as you get to Sydney. As an Australian we can do online pre-approval on the Sydney thai consulate. Have a look you may also be able to
For the 60 day visa your better off to make up flights within the 60 days. Although you can and rarely is it declined you can get the extension the visa is for 60 days. Look up dates and flights to suit. Sydney does not ask for proof of booked flights. Of course there will be people who have done dates outside of 60 days but I personally preferred to play it safe.