Regarding tank numbers, there's been a lot of discussion regarding how many Australia needs. In order to answer this with any relevancy one needs to understand how tank are actually used in Australia.
At the moment the Army has two tanks squadrons. Quite obviously this is not enough for the three Beersheeba brigades, so unless someone makes a very unexpected decision a third tank squadron will be raised for 7 Bde (2 Cav/3 Bde will own a tank squadron by the end of the year, ready or not). This doesn't necessarily mean more tanks will be bought - it would be possible to sustain three squadrons with the current number of tanks as long as tanks were rotated from brigade to brigade as part of the force generation cycle. However, this would be a terribly bad idea and I would be amazed if another dozen or so weren't bought to equip the third squadron. This will likely occur either as a result of the coming white paper or be purchased as part of Land 907-2 (the tank capability assurance program which will see the upgrade/replacement of the current tank fleet to keep them in service and competitive out to 2030).
Essentially we can expect that each brigade will have its own tank squadron by 2018. However, all the current modelling and experience has shown that this is not enough based on how tanks are going to be employed by the brigades. Tanks, as anyone has read any history will know, should be applied en masse. Due to their limited numbers, tanks in Australia will always be the main effort that will be unleashed at the decisive place at the decisive time to achieve decision.
The question is can a single squadron create enough mass to be decisive? Particularly when the squadron is diluted to serve other purposes? For instance, every single brigade commander from now until eternity is immediately going to place one of the tank troops in the brigade reserve. It has always happened and will always happen. So already the Squadron is down to two troops. Do you split those two troops up as well to provide tanks to support more than one combat team, or do you keep them centralised to enable a decisive effect?
There's also the massive issue of CSS. The A1 ech for the tank squadron is designed to support the squadron as a whole. While you can split tank troops off to support other combat teams, you can't split the A1. The general rule is you can split the tank squadron once (ie, have one troop supporting another combat team and keeping the other ten tanks centralised), as long as they share a boundary. Trying to split the tanks further (for instance, assigning a tank troop to three different combat teams) is simply not possible - the A1 won't be able to support it. Essentially, a single squadron isn't enough to be decisive as part of a Beersheba brigade.
It's worth pointing out here that the Beersheeba Brigade, as it currently stands, is not designed to be fought as is. It is a designed to enable the raise, train and sustain of the various components that would then be combined as necessary based on need. Hence the concept of the 'Reinforced' Combat Brigade. If a contingency came up that needed more than a single squadron of tanks in the brigade, then tanks from another brigade would be used to reinforce. Obviously this is not sustainable for ever, but it is a start. All this essentially means is Army won't be able to justify buying lots more tanks, based on the needs of a single brigade, because it will simply be told to pool tanks when needed.
What then is a realistic sized tank force? Personally, I think the best we will get is for the tank squadrons to be enlarged to a four-troop construct. If the A1 was also boosted, this would then enable tanks to be split off from the squadron for other tasks (such as brigade reserve) and still maintain a large enough mass to be decisive. I think the way to justify this is for the 'fourth' troop to be designated the SEQ troop, equipped with mine blows and tank rollers, and be considered part of the manoeuvre support capability and not part of the gun tank capability. But engineering vehicles are a whole different kettle of fish...
I guess a point I am trying to make is arbitrarily saying 'we need XX number of tanks', without understanding how they will be used is pretty pointless (albeit good fun). Defence is a zero sum game, and a big pot of gold is not going to fall in our laps any time soon, so increasing one capability somewhere has to come at the expense of reducing another capability somewhere else. It is certainly not easy, and simply saying 'buy more of everything' isn't a very useful answer.
Sorry for the ramble.