What are you trying to SLI, and why? You realize that SLI is, for all intents and purposes, dead, right? Nobody is really creating SLI profiles or including SLI support in the majority of games anymore because mostly it's simply not needed.
So, what are you actually trying to do and why, if you don't mind my asking?
Honestly, you'll need to go back to 2014 or so to make this even slightly practical. Multi-GPU solutions are effectively dead now; they never scaled all that well, but in a greatly increasing number of games, the benefit is either nothing or even negative.
Definitely not worth even ATTEMPTING to do SLI with two GTX 960's. Fortunately, getting better performance is going to be pretty easy because just about everything outperforms that card these days.
For the prices in Australia, you don't have enough to do a platform upgrade AND upgrade the graphics card to a model that is going to give you what you need. So I would recommend that you do THIS first, and then save the rest until you have enough to do the second part. By then though, there may be much better options on the table because there are new Ryzen parts coming supposedly in November or December and depending on when it is, there might even be 10nm Intel desktop parts by then, although I think it's doubtful that anything worthwhile coming from Intel will be seen for quite a while.
Later, the motherboard, CPU and memory upgrade when you can afford to throw another 600 bucks at it, including the 350 you're not going to spend right now and put away towards that 600 bucks, so really only another 250 bucks. Something LIKE this, not necessary SAME as this, considering there will probably be better options by then if it is more than two months away.