Hi Rhiannon!
I have to agree with my fellow aussie Chelle, far north Queensland is great! I did a Contiki tour up there some years ago, as far as Port Douglas (an hour north of Cairns and also worth a visit!).
It is pretty warm in FNQ all year round! March-April the average min. is around 20 degrees C, and max around 30. And I think ALL houses up there would have airconditioning, just as I imagine pretty much all houses in the UK have some form of heating (but I could be wrong!)
The wet season is December to April, so you'll catch the end of it...it's kinda nice even when it rains it's like a warm shower, and all the frogs start singing...it sort of seems to compliment the whole rainforesty thing! I'm afraid it is stinger (Box jellyfish) season as well, Oct to April...the beaches have nets to keep them out so as long as you swim where the signs say you'll be fine. The beaches are beautiful...Palm Beach, Trinity Beach, Ellis Beach...
Again I agree with Chelle, the Kuranda Scenic Railway is a must, as is the Great Barrier Reef and of course all the islands. There are heaps of tours and cruises, and you can dive or snorkel if you're game! There's Carrowong (sp?) Fauna Santuary (the night tour is good!) and a Crocodile farm (Hartley's Creek) for the kids, plus closer to the city is the Botanic Gardens and the Centenary Lanes boardwalk with rainforest, a freshwater lake, BBQ's and a playground. The markets are wonderful, Mud Markets if you like crafty stuff (near Marlin Marina) and the Night Markets are open every night (good cheap food).
Like Chelle, I could go on and on...oh actually I think I already have!
How did you arrange the houseswap? Are they friends or rellies? (Btw have you seen that miniseries called The Swap? It's about a London couple who arrange a houseswap over the internet with a guy in Perth Aust.!!! Not bad actually, although some bad inaccuracies about Perth and I don't think it was filmed here or even used many Aussie actors (some of the accents were a bit dodgy!) There is no "Perth University" for one, and we cracked up at the part where the uni receptionist answered the phone "Perth University, gidday". Honest, we really don't talk like that!!!!)
Let me know if you think of any other questions (if you dare!!!)
PS When you asked about stopovers did you mean other Aussie places or on the way over here?