Hi dyllah,
No need to use travel agency.Its quit simple like S'pore.
Juz get an airline pkg free n easy that could provide you accommondation at Gold Coast.
From Brisbane Airport you can use the hourly shuttle service buses to your hotel or apartment.
Upon arrival you can plan which ever WORLD YOU LIKE TO VISIT & they will jolly well help you -just zap in your card :)
*Look out for any public holidays in Australia coz during our trip my old schoolmate which happened using free SIA ticket landed up with expensive accommondation & car rental - because it was Queen's Birthday.
For June-Aug since it is near to the cost, the weather is warm in the day but cooler in the night abt 15-20c
No need to bring winter jacket, takada snow-Wind breaker will do :)
Psst....there are numbers of Asian market that provide you with local food eg Singapore made frozen Prata)- Just like Sheng Siong !
Check this one out-
http://weather.yahoo.com/forecast/ASXX0047_c.html