It's a long way from the Gold Coast to the far north. So with just 10 days, I wouldn't recommend driving the whole way. You'll want to spend, at the very least, a full day (2 nights) on or near Fraser, preferably two or three days. It's a big place.

To combine the Gold Coast, Fraser Island and the reef, you might consider including Heron Island to your itinerary. It'll save having to fly or drive to the far north. Heron is on the southern end of the Barrier Reef and offers fantastic snorkeling and diving. It's not far north of Fraser island. On the Gold Coast you can venture a short ways inland to the beautiful mountain rainforests of Lamington National Park, maybe stay at O'Reilly's or Binna Burra guesthouse in the park.

If you do go to the far north, I'd recommend going to the Cairns area rather than the Whitsundays. More to do and see.

I second Ralph's statements about Fraser and the size and distances involved.

Assuming you are from the US: would you try to see all of the east or west coast in one trip?

You can squeeze in as much traveling in Australia as you like but you'll not see that much of the country except out of the window if you try to do all this.

Thanks Ralph and Alan. Looks like I'll give the far north a pass.
Ralph - Thanks for the reco on Lamington, think it'll be a good addition to our itenary.

One other qn - for travelling by road, what do you recommend between hiring a car vs travelling by greyhound buses?

The bus is generally a little quicker for longer journeys, give little flexibility but saves on your energy as long as you are able to travel comfortably like that. For the car it is the other way around.