With no disrespect intended - I think you're missing the point.
If we're talking hot war - they don't need to invade Indonesia - you're thinking land or land air campaign.
The PLA Navy are quite capable of denying Australian sea-lanes, interdicting or simply harassing shipping.
In fact they're transitioning right now from being a green water navy, to a blue water navy.
They have a nascent carrier capability to project air-power at distance and in addition, operate nearly 70 diesel electric and nuclear boats.
China could effectively sail right around Indonesia and any other country in the way and make things very, very difficult for Australia if it really needed to.
They don't need to put a single PLA boot on Australian soil, or anywhere else in South East Asia to do so.
In my view, that's the most likely scenario for a shooting war - a drawn out air-sea campaign at long distance, with isolated vessels sunk - jets shot down BVR - and if they got really irritated - drop a cruise missile or two with a conventional warhead on one or two Australian bases.
Not all out total war.
The yellow hordes aren't going to come sweeping over the Timor Sea in landing craft after they've blitzkrieged their way through every country between us and them.
What have we got that they want - some food producing land, a lot of mineral resources, and a few irritating US bases?
That would be a similar scenario to the one facing Japan during WW2, and why the Japanese were never seriously going to invade Oz.
The Japanese Naval high command was gung ho - but the Army said `don't be crazy, think of how long the supply lines would be.'
I think the Chinese are far more likely to get so cocksure that they'll feel they can reach out at long range and punch us a couple of times to remind us who's boss in the neighbourhood.
I agree with Hugh White's assessment.
We need nuclear powered boats with conventional cruise missiles, plus small diesel electrics for the work that's currently being done in the South China Sea littoral waters, and as many underwater UAVs as we can afford.
Not more surface ships and certainly not the Collins successor.
In addition to ABM defence interceptors, we need more F-35s and LRASMs.
And given the lead time we need to start thinking right now about a domestically developed nuclear deterrent.
EDIT: Noting that it is Wikipedia:
The PLAN's ambitions include operating out to the first and second island chains, as far as the South Pacific near Australia, and spanning to the Aleutian islands, and operations extending to the Straits of Malacca near the Indian Ocean.[127]The future PLAN fleet will be composed of a balance of combatant assets aimed at maximising the PLAN's fighting effectiveness. On the high end, there would be modern destroyers equipped with long-range air defense missiles (Type 052B, Type 052C, Type 052D, Type 051C and Type 055); destroyers armed with supersonic anti-ship missiles (Sovremenny class); advanced nuclear-powered attack and ballistic missile submarines (Type 093, Type 095, Type 094, Type 096); advanced conventional attack submarines (Kilo and Yuan classes); aircraft carriers (Type 001A, Type 002 and Type 003) and large amphibious warfare vessels (Type 071 and Type 075) capable of mobilizing troops at long distances.