Hmmm, would there be extensive urbanisation along the Murray valley, with perhaps a major city state in the location of OTL Albury-Wodonga?
The Murray Valley, particularly the middle Murray and the lower Murrumbidgee, are going to be extensively urbanised. Not necessarily
large cities, but lots of them. *Australian agriculture is going to be quite productive per acre, even without irrigation. In a place with enough water for drinking and managed wetlands, there's going to be a lot of people living there. Possibly a few other areas as well, but the Murray Valley will be a thickly-populated region.
1) Well, Bugis did reach places as far as Madagascar and South Africa IOTL, so I don't think that would be as much of a stretch like you pointed for them if it's just for Tasmania. The ancestors of Madagaskar Malays came to the island with even less advanced naval technology compared to 15th century Bugis....
Actually, it is quite a stretch for their naval technology. The Indian Ocean is quite easy to sail across once you've figured out the monsoon patterns. (It's the easiest of the major oceans to sail across). The way the prevailing winds blow in Australia, though, actually makes it a considerable pain to sail south along either the east or the west coast. Exploring the northern reaches is pretty easy - it is in fact a natural extension of following the monsoons along the rest of the Indian Ocean - but going further south means you're working against the prevailing winds the entire way. The winds blow you north (if you're lucky), or into the shore, if you're unlucky. Having reefs along much of the northern stretches doesn't help with exploration, either.
The easy way to explore Australia with sailing ships is to start at the south and work your way north. It's no coincidence that most of the European exploration of Australia worked this way. The Dutch found it easy to explore Australia because they were coming from the south and working north (or keeping on going east to New Zealand, which also works). Whereas the Spanish and Portuguese had been sniffing around the north of Australia for a while, and didn't make it further south.
3) I don't think I get your point here. They were enthusiastic explorers, so why won't they be motivated if it's just to explore ?
Partly because of the natural barriers, as mentioned upthread, and also because they don't seem to have done it in OTL. I'm not aware of any mention of the Bugis making it as far as Cape York, even - although they may well have been occasional visitors. Certainly, even if they were at Cape York, going all the way down the east coast
is a difficult accomplishment.
Yet they didn't do it in OTL, if they didn't do it then, why would they do it when the areas they did visit in OTL are the same??
How can you be so sure ?
I'm not sure whether they did it or not personally too. I saw it on one of the books I read back then, that the Bugis did sail as far as Tasmania IOTL. Of course, I have yet to hold any confirming proofs. But nor that it has already been confirmed that they didn't either....
If the Bugis had been given sufficient motivation, they might have been able to work out a way to explore further south. There's no increased ATL motivation for them, though, and I can't find any source which indicates that they made it past Cape York or the northernmost reaches of Western Australia. There's even considerable argument about exactly when the Bugis reached Australia. Certainly they made it by the early 1700s, but this is a century or so after the Dutch are going to start exploring from the south. Some people contend that the Bugis had been exploring northern Australia since the mid-1400s, but the evidence is contentious.