Well for 1080p gaming, Intel is better than Ryzen. However if you plan on streaming while gaming or perhaps video editing, Ryzen is the better choice for the money. Then you need to consider if you are going to overclock. If so, then you can look at AIO (all in one) boxed water cooling vs. air cooling.
That's your core chipset build: CPU, motherboard, memory, CPU cooler. Then the case. If your ambient temps there in Australia are mostly warm then you want a case with a good air flow (like having two intake and exhaust fans, with one exhaust out the back as most cases have by default and one on top). Then add a 2TB or 4TB hard drive for file and game storage and possibly a DVD/BD drive or burner and you are good. Use that SSD for your operating system and most used apps.
Think about what you want out of your build then go from there. That's the way I plan builds. The fact that you have already chosen the GPU and monitor means you want to make sure that GPU is powered by a decent CPU that won't bottleneck it. With all that said, 1100$ AUD is about $875USD and since you got the two biggest single expenses out of the way (GPU and monitor), you'll have no problem finishing it.