Well being one of the few Aussies here on the forums at the moment, I think I feel qualified to answer some of your questions! :)

Cairns and Port Douglas, you can expect to be reasonably hot and humid. Weather should be fine and warm on most days, you might just start to get a bit of rain though as the wet season will be thinking about kicking in. Although with the weather so screwy all over the world these days its anyones guess.

Cairns is a nice little town, very tourist centric, so you should be able to get in on some great tours. If you like tropical rainforest type stuff, book a day or two on a guided tour of the hinterlands. You will really enjoy it. Track down one of the places that does harley tours and get in on some of that action as well. The guys are very experienced riders and you'll get real value for money. Do a search for the skyrail train in cairns as well, its a breathtaking experience.

For the most part you'll find aussies are very laid back and easy going. This should make your trip extremely easy and a lot of fun. Hitting up Sydney after your laid back tropical adventure will bring you back into reality though. Its a very fast moving town and its expensive, on the plus side, if your wife enjoys shopping you will have a blast there. If you do Sydney first and then head up North the difference will be immediately noticeable.. :)

If you are heading south past brisbane to the Gold Coast I know of a really great cigar shop that you can visit. PM me for the details on that.

As for the Koala's.. Well the good news is they look soft and cuddly. The bad news is they are quite grumpy, ill mannered and fairly vicious. They sleep a lot of the day away and just don't seem to like being woken up! I have heard though there are quite a few more timid and well behaved ones in some of the wildlife sanctuaries.

I've never been to Auckland in NZ, but I assume from North Island that's where you'll be heading. There is one place I've heard of though which sounds like a real must check out venue. Its called 'The Ice Bar' and yep you guessed it, it's made entirely of ice.

Well if you have any more questions, let me know and I'll do my best to help you out.