Hi Dachlostar,
I am a travel agent, and for your flights, if you can leave before the end of March, it is usually cheaper, as April is the start of the 'shoulder season' so it gets more expensive, plus there are ususally easter and school holidays in April so it's a busy and therefore expensive time to travel. There are really 2 options for booking flights, you can wait for a while, say November/December, and see if there are any earlybirds, or you can book now at the best available flights. I am in Sydney, so I will gladly send you a quote if you like you can just PM me and I can send you my work email and I can do it tomorrow. No obligations of course, but I can at least give you an idea.