The basic idea was federation at the beginning.
As for the party discipline idea, it doesn't necessarily have to form. In the US, regionalism was able to hold sway over party identification for as long time, because the differences in development prevented any rigid party from achieving electoral victory. Without the moral issue of slavery or the sectional conflict of the civil war, I think that party discipline could take a longer time to form (if the senators use their powers well). Especially with the gulf between Fiji and Australia or even New Zealand and Australia. Just because regionalism failed in Australia in OTL doesn't mean it couldn't hold sway in this one.
Well a couple of things. If we're talking 1901, then there are a lot of things running against trying to equal up the population numbers. In New Zealand, for instance, their population at the time was only about 900 000. What's worse is the Fijian population, which was a mere 120 000. Meanwhile the population of south-east Australia was about 3 million out of about 4 million. Furthermore, at this point in time, I think it's safe to say New Guinea won't be a state as we're only talking the south-east quarter of the island & that part was Queensland territory for just around 10 years. Not only would Queensland object to its "colony" being granted statehood, but I'd dare say all the other potential states would as well.
The next issue, I'm sad to say, is race. Not only were the Australian Aboriginals treated as tenth class citizens in their own country, but those natives of New Guinea & elsewhere, including Fiji, were looked upon as a lower class of humanity as well. In fact a perfect example of this treatment of South Pacific Islanders is the case of the Kanakas (see this
Wiki article for details). So Australia's racist attitudes of the period is going to ensure that it's highly unlikely that neither New Guinea nor Fiji are going to be offered statehood, but them becoming an occupied territory or a protectorate territory maybe a different story. In this instance you can probably add in the Solomon Islands as well. Mind you Britain would have to go along with such measures & they were far from happy when Queensland grabbed New Guinea when they did. Having said that, about possible objections from Britian, if New Guinea, Fiji, & the Solomons did become territories of one kind or another, then there is the potential that they could be granted statehood sometime in the future - say from 1945 onwards.
So that leaves New Zealand which was an actual OTL candidate for statehood. In fact they're mentioned in the Australian Constitution as such. So we could mingle a little with New Zealand's domestic politics & give them a PM who is prepared to join Australia unlike the OTL PM who had visions of grandeur about a NZ Pacific empire. Having said that, however, the south-eastern region of Australia will still have the numbers as they'll outnumber everyone else by about 1 million people. So they'll still have the majority in the House of Representatives.
The other main issue here is party discipline. Unlike the US, Australia followed a different path thanks to major political influcences coming from being a member of the British Empire (essentially the Westminster System). So we didn't really get the chance to develop an independent system where there's a seperate President/Executive from the Legislature/Congress. Instead in our system, it's vital to control a majority in the House of Representatives in order to form executive government. Furthermore, thanks to the development of the Labo(u)r Parties, here & there, & most certainly in Australia, means to say that ideology becomes more important for political parties, & their members, than regional politics at a nation level.
So when one party decides to get its act together, in regards to party discipline, the others will follow suit not long afterwards as it'll be soon realised that gaining, & far more importantly keeping, government is made far more easier. And considering the members of the Australian Labor Party all came from a unionist working class background, at a time when there where cries of
Workers Unite!, that party discipline will develop very early in the peice, yet not through any enforced party authority at first, but through an agreed mutual consensus. Once that happens with the Labor Party, then, as I said, the anti-Labor Parties will either follow suit or fall apart. Mind you it took about a decade for this to happen, as is evident by the rollercoster ride early Australian governments had as they came & went about as fast as they could print the new letterheads on the stationary. Consequentially, I'm affraid, in the Australian context, party discipline will pretty much repeat its development in this AH Australia, so there'll be little change overall on this issue, especially considering the experience of the New Zealand Labour Party pretty much repeated the Australian Labor Party experience on such issues.