Hi novice and welcome to a groovy forum.
It's difficult to ask advice like this as it involves a lot of consideration and one of them is how much is your budget.
I built my own and one of the methods used was to look at specialist pc builder websites and the configurations they were offering.
I note you are in the antipodes but here's a british firm that builds pcs : PCSPECIALIST.CO.UK - Custom PCs, Custom Computers, Custom PC, Desktop PC, Custom Built Computers, Gaming PC
You may have similar companies near you.
If you look at that page you will see three gaming pcs built to a certain budget, if you go into the page with the budget that's just over your's you will see that you can alter your choices of GPU or CPU, RAM etc and how that affects the cost.
As this company has got to build that pc they will only offer you upgrades in the drop down menus that are compatible with the mobo and the rest of the rig.
Using their components list as a guide, price up the parts locally to you and see what you can build it youself for.
This will take some time and you should end up with two or more lists of pc components that suit your needs and your pocket.
Personally I would also read reviews of each of the components and see, for example, whether tech sites say that one motherboard is better than another, or one HSF etc
Eventually you will have a good idea of your choices and alternatives.
Then post it on here and invite comment.
This is a lot of work but well worth it.
Let us know how you're getting on, John