So, that leaves a question for Australia, what specific shape (in terms of time, rates and events) will collapse take here? After all, both Europe and America appear to be entering a contraction phase of catabolic collapse, authoritarianism (not necessarily fascist) is the likely end point for much of Europe if current trends continue and America, as the John Micheal Greer said, will likely become a bubble-bust economy and potentially face insurgencies/cross border raids. Here the crises that are affecting Europe and America are relatively (still present) minor and our economy is doing relatively well (due to China and certain banking practices). So immediately now, differences in the shape of collapse are apparent between Australia and the rest of the West. America, which is the top imperial power and with what could turn into a very hostile migrant nation to the south (Mexico) with iridescent claims, is in a completely different situation. Australia is a regional power that is allied to America, but has an independent military, with the potential hostile migrant nation (Indonesia) far away (Perth to Jakarta is5592.47km) from any fertile land in western Australia and across the sea but has no demographic support in Australia. From Jakarta to Cairns its 4396km and by sea its longer since you can't go in a straight line. So we can't use America as a model.
The Roman collapse doesn't really have anything similar to Australia's situation, partly because of the geography and in a specific way in regards to military. Everywhere in the Roman empire was close to somewhere else, even England was really close to Ireland, Scotland and mainland Europe (the English channel is 31-240 km wide) while Australia (at least the fertile areas) is thousands of km's from anywhere else. That's the main geographical difference, there are a few others. Militarily, Rome's 'vassals' states mostly provided cheap low quality manpower for auxiliaries, i.e. everything but heavy infantry (that was the legions), or lower quality troops than the legions. Australian troops in WW1 statistically in terms of capturing were twice as effective as British troops, so Australia provided higher quality manpower than what Britain had indigenously. Think of it like this, very few African nations have an effective military (see how many rebels it takes to beat most of them) which is closer to the Roman model (its still different) while Australia has a fully functioning military that can operate independently (at least locally) from America's though it requires support from the outside for parts currently. So quite a few events that happened in Rome's empire (like the sack of Athens) and that will likely happen (or could be considered to be happening) in Africa won't happen here.
The effects on transport will be different. Australia is an almost entirely coastal nation, even if the practical definition of coastal returns to being within 5km (probably won't, changes have happened, more likely 10-50km depending on terrain), so the resurrection of sailing will dis-proportionally benefit Australia compared to Europe, America, Africa or Asia. Transport will decline everywhere, but here it will recover far earlier than otherwise and reach a fairly high level (relative to historical cases). This is a significant cause of different rates and times. Now, transport decline (specifically that needing oil) is likely to hit Australia earlier than other countries because of our remoteness and the impacts of that will be on a different time frame than in most of America, Europe or Asia.
Destruction of civil society is highly unlikely here, due to our political systems incredible stability (part of its design), lack of nearby foreign invaders or conquerors to cause chaos or wreck institutions (like courts or police) and an effective military. Feudalism will almost certainly not appear because of this, since it only makes sense when civil society and rule of law has disintegrated. There also isn't a lot of (serious) anti-government rhetoric or feeling around, Australians by and large aren't revolutionaries, radicals or anything like those groups that are willing to directly attack the foundations of government. The government will disappear from some areas, mostly the outback, but its highly unlikely to disappear completely in the heavily settled rural areas and won't leave the cities without extreme problems appearing.
The collapse here will look very different than in the rest of the West, Africa and the East. The isolation will speed up certain things (such as de-linking from the rest of the world), the coastal nature will affect others and so on. In 2010 I read an article (unfortunately I've lost it) which claimed that Australia would become like Europe in 2012, which hasn't happened. The mistake was in seeing Australia operating on the same time frame, events and context as Europe, which it isn't. You can't say that because it happened there, it will happen here shortly. The inverse is also true. Australia is on different path than other places of the world, like how Africa, South America or Asia are. Later as collapse furthers, Australia will still be in a different position. Comparing ourselves to Europe or America is at best only marginally useful for figuring out the specific shape of collapse in Australia.
Africa is recovering from colonialism and is in the process of forming viable nation-states, the cultural factors that caused tribes to hate each other are incredibly malleable and so far its getting better. It is certainly more peaceful (yes its still violent, but less so) that what happened in Europe, which is surprising since the process which took centuries is now taking place within a century. Overshoot might not actually stop this process, since neocolonialism's end will increase the resources available to Africa and while certain aspects of the current nation-states probably won't survive, like democracy, an African form is quite likely to appear. The East is also in a different position, with combat over water between nations, very close neighbors and the rise of a Chinese superpower. It is in the process of equalizing with the West and while it will decline as well, it is again on its own path.
Lets break up the entire process of collapse into sections. Think of these variables as a line that goes up and down, yes its abstract but it will help visualize whats happening, if you've read limits to growth then you've seen what I mean. The economy can be shown as one big variable, made up of agriculture, industry and service. Violence/instability can be divided up into external and internal instability. International and internal transport are also separate, with internal being divided up into local, regional and national. You can add a few more.
Economically, the graph will have an overall downward trend which will probably unambiguously start either near the end of this decade or early next. Depending on the factors of selling resources and how they change. According to the CIA fact book, agriculture currently makes up 4%, Industry 21.1% and services 75% of our economy. Obviously agriculture will go up, probably to an endpoint of around 50-60%, while services will drop quite dramatically. Industry is quite likely to also increase, not by a lot, lets say to 25-30%.
International transport will simply decline until stability has been achieved and sailing boast are widespread enough for it to start to recover. The problem is piracy and instability will likely make it quite hard to trade/travel large distances even if you have a sea worthy boat. Internal transport will decline and then pick up as sailing ships start coming back in large numbers, might still decline later on due to further economic and resource shocks.On the national scale, it'll follow that pattern, decline as air travel and cars disappear, then pick up as sailing ships (maybe trains and zeppelins as well) expand. Regional (so state or interstate) transport will decline quite far, small coastal ships will help and expanding use of bikes (cargo included) and velomobile's would help,especially in inland areas, here is also where any expansion of rail will help the most. Local transport will definitely decline with the automobile, but since almost everyone can walk it has a set lower limit, though horses or bikes will be needed in many rural/ semi urban areas . Bikes and public transport (e.g. trams) would help here the best.
External instability, e.g. wars, invasions etc, is unlikely to be a major problem simply from the vast distances from the settled parts of Australia is to anywhere else. It'll affect Australia indirectly vie economical affects. Internal instability, e.g riots, civil wars etc, is much more likely, mainly riot and civil unrest since a civil war would require a very different country. A feedback loop is created with external instability creating internal instability or vice versa, say by a civil war stripping border guards which causes increased raids, so the low external instability will mean that internal instability will stay quite low.
That's a basic outline of collapse in Australia.