That's a nice decision to commit to the project that has already seen such a massive investment initially. IMHO Australia is one of the few countries in the world which has absolutely no enemies, considering that all the immediate regional military forces, Indonesia, India, China and Russia have cordial relations with them. While Aussies take American assistance in defence, they are a friendly country generally to all.
However, they are rich in resources which is what puts them at the risk of getting 'democratized and given freedom'
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While no one can predict enemies, it is always best to take precautions. And for Australia which has such a robust economic structure, they should invest in at least 150 JSFs and consider more of missile defense.
Look at the Chinese for example; while they lag behind USA in terms of defense platforms despite their rise, they chose a smart and cost effective method to circumvent the strategic gap: tactical missile, a whole storm cloud of them. If it is a carrier attacking, rain missiles. If is in a US Navy squadron attempting to infiltrate into Chinese airspace, rain cost-effective short-medium range SAMs.
It is a smart way of ensuring that they have the baggage to attack but very few will risk their necks invading your country. Even with a small air force, if you invest in tactical missile technology, it can get you a lot of long term results. While anti-missile systems are available, the can be overwhelmed with a barrage of them. That's what the Chinese have done and that is very appreciable; something I'd personally love to see our military adopt: A blanket of SAMs, SSMs, SShMs along all our peripheral regions.
You being an island nation, should consider SAMs and SShMs heavily for now.
150 jets may be enough to hold someone off but these days you never knew how alliances turn into enmity.
All the best.
