I think the easy access to huge swathes of good farmland would be a major factor in Victoria gaining an economic dominance if it was settled in 1803. The Sydney basin was hemmed in my mountains which were not crossed for 25 years after the colony was founded, but west of Port Phillip Bay is a big open plain with little in the way of obstacles which IOTL was occupied by pastoral concerns with remarkable speed.
In part, but only in part. The Sydney basin was not immense, but it was large enough to still attract
some free settlers, and in practice there's only a decade between 1803 and when the Blue Mountains were crossed by Europeans in 1813, so it's not that large of an advantage.
The more fundamental question is what sort of colony is being run here? If it's just another convict settlement, well, the number of convicts being sent out from Britain is unlikely to change as a result, so all that means is that the same number of settlers are spread over a larger area. Some increased economic dominance for Victoria
vis a vis New South Wales, but not that much of a larger population continent-wide, if any.
The wild card is, of course, gold. Will there be an earlier gold rush? Perhaps, perhaps not. A few points to consider:
Gold had been discovered several times in Australia before the first gold rush in 1851: at least 8 times in New South Wales, several times in Victoria, possibly also in Tasmania, and an active (though small and quickly exhausted) gold mine in South Australia. But news of these had mostly been suppressed, and it's quite possible that a penal colony governor in Victoria (or the New South Wales governor, if it remains part of the same colony) would try to squash the news in the same way.
Even when the news wasn't suppressed, it
still didn't trigger gold rushes. As late as 1848, news of gold finds in Bathurst were published in the main Sydney newspaper - but no gold rush yet. It could well be that the example of the California Gold Rush was required both to act as general inspiration
and to create a large enough class of people who were prepared to travel around the world in pursuit of gold. California was remote from the perspective of most gold rush migrants, but Australia was even
more remort.
There's also a question of shipping. The Victorian gold rushes led to the pioneering of new shipping routes - which essentially cut the time to travel to Australia in half - but would these be feasily discovered and used three or four decades earlier? (I don't know, but it makes an important difference.)