Too ambitious. Unless you are flying First Class with the lie flat seats that convert into actual beds, you are going to have jet lag something fierce. I am a retired flight attendant. When I flew from LAX to SYD in coach, I never actually got fully to sleep at any time in the 14 hours aloft. Your first day on the ground in Australia will probably be in bed trying to get to sleep. Your itinerary reminds me of a choir tour I was on in college. We had 2 hours free in D.C. and we all voted to go to the National Gallery of Art (this was in the 60's, so no Vietnam memorial or other later constructions). Most of us had never been to the National Gallery and had no idea how large it was or how much artwork was on display. Our choir director told us (tongue in cheek of course) "you can see the whole thing in less than 2 hours as long as you don't look at anything."
Per Google Maps, the shortest car route from Sydney to Brisbane is the coast road. The views are so gorgeous you will be stopping to look and/or take pictures frequently, and remember it's almost a 600 mile trip. I can't believe you aren't staying in Sydney more than a day. It is one of the most beautiful and fascinating cities in the world.
I would definitely rethink the itinerary and delete some of your stops and save them for next trip. I would not go to Brisbane if I didn't have time to go to the Lone Pine Zoo/Animal Sanctuary. It may be your only chance to hold a koala. They are wonderful (even though they smell to high heaven due to their diet of eucalyptus leaves).
Australia is a great country and the people are incredibly friendly. (You know it's one of the few remaining places where we are truly welcome.) Take time to savor the beauty of the country and its people.