It's our 1st visit to AUS and we need some advice. We'll be coming from the US for about 2 weeks.

Our plan right now is to fly into Sydney, spend 5 days there. We would like to go to Melbourne...we have extended family there.
What's the best way to get from Sydney to Mebourne? Rail/Car/Plane? how long/cost, etc?

Is there anything we should definitely do while we're down there. Plan on doing the Barrier reef. Anything else a must do.

We're in our early 30's and like to do active/ sporty stuff. Not really into the club scene but enjoy good restaurants and pubs.

TIA