I have no idea what they would cost in Australian dollars since i am in Canada :P.
I would add the most dosile fish first and the most aggressive fish last. I would properly add the clowns last since they can hold their own and they will generally gain up on other fish. I think the flame angel is the least aggressive so I would add him first. Than probably the six-line wrasse and the purple dotty than the clowns last. This is just my best guess I would talk to your lfs
i would without a doubt add the clowns last. Word of warning clowns have a history of biting their owners. You might have a few thumb wars with them. They aren't big enough to cause any damage. If they really really like your tank and are feeling naughty they will probably lay eggs since they can change their sex at will.