I'm just gonna share what I remember from the actual Bushfire Relief ads, and other ads on disasters I've seen on tv and stuff.
Use images of people and Australian native animals affected by fires, rather than images of buildings. We especially like images of Koalas and baby Kangaroos being supported/cared for by our firefighters.
Put a few simple words in big text, like "Do ypur part to help." or a raw statistoc on how many cattle died, or how much farmland was affected, or how much national parkland was lost. Leave the fancy words for smaller text paragraphs underneath, expanding on the bigger text.
Use desaturated pictures over full colour. Grayscale is fine too, but only if it's a really light picture whoch lots of details to stand out.
As for culture, we 'love' our firefighters and farmers and native animals. We're NOT a fan of our PM, to the point he turned up unannounced in a town affected by fires last year and got told where to go.