One of the very rare things I agree with Sepp Blatter's idea's is a rotation policy in giving the regions the right to host a World Cup.
2010 will either go to Morroco or South Africa, 2014 in all fairness should go to South America, so should the 2018 WC go to Australia since this region has hosted one? In all fairness yes since Europe has had their fair share of tournaments hosted. If not in 2018, it should be in 2022.
I'm not to sure on stadia requirements, but Australia has the SCG, the 'Gabba and the MCG as main stadiums to host matches have have capaticaty of 40,000+.
Stadiums have available to use:
Telstra Stadium (ex Stadium Australia and where the final would be held)
Telstra Dome (perfect with the roof over the top and the seats moved in)
Suncorp Stadium (Brisbane)
Football Stadium (Adelaide)
Dairy Farmers Stadium (Townsville - but needs to the grassy hills to be turned into all-seaters)