Planned custom gaming PC,

That motherboard is designed for the older Sandy Bridge chips. To take advantage of the new features in Ivy Bridge, you will want a Z77 board.

That GPU is last generation stuff as well, the HD 7850 gives similar performance with a lot less power consumption and it's probably cheaper. The HD 7870 is even better if you can afford it.

No games will use more than 4GB RAM at the moment, I would get a max of 8GB.

You will never need 2 GPU's for gaming on a single monitor, if you wait until your single card can't handle it to upgrade, buying a second one won't be wise. I'd just put your cash into one good card.

That PSU is fine for SLI but I wouldn't recommend SLI to be honest, so a 500W PSU would be my recommendation.

ok, how about a P8Z77-V-LX
http://www.asus.com/Motherboards/Intel_Socket_1155/P8Z7...

and a thermaltake spacecraft:
http://msy.com.au/product.jsp?productId=8208
this comes with a 500W psu as you suggest (this also saves about $80), are thermaltake psu's low/mid/high quality?

for the GPU the difference in price is about $10 dollars, for a small amount of extra performance, so i think ill just keep the gtx 570.

I think I will also at least initially go with 8GB as you suggest, I'll have 4 slots so i can easily upgrade if i want.

Thermaltake PsUs are mid-quality

And hopefully it will continue to do so for a very long time, especially since Thermaltake is mid-quality but even the "poor" power supplies will work more often than not ootb. The difference between good and bad manufacturers is more just the likelyhood of failure (or how long before it fails).

The experts on these forums are simply trying to steer people to the least likely psu failure, because that is something no one wants to happen in their system.

I'd go for that modular 520W Seasonic PSU at $59.99. Seasonic are top notch, it's a steal at that price.

EDIT: It's on US Newegg, just realised you're in AUS. Seasonic are a good name to look for though. Antec, Corsair and XFX too. Be Quiet are usually good as well.

Yes, you don't want to hijack...

But to answer anyway, if you want to be safe (and with a beast of a machine like that who wouldn't?) I would start my own thread and ask for advice from someone who knows more than me. Basically other than trusting Seasonic and Corsair I don't have enough experience to give good advice.

To the OP: looks like you're on the right track, take the advice offered on these forums and you will do well.