1013, the figure you mention for -400 second officers is a lot...until you consider that most of those pilots had the experience and licences to be captains when they joined. It is also noteworthy that most other longhaul operators utilise up to two captains and two F/Os for the same sectors as those where QF uses 1x captain, 1x F/O(cruise captain) and 2 S/Os. It is merely QF policy to recruit all pilots to the position of S/O, assigning them to type on joining day. S/O pay is a defined as a factor of captain's pay for the given type.
So...it's a major saving in terms of pilot costs, enabled by the fact that many are prepared to accept less money and slower promotion in order to live in and work from Oz in a company like Qantas. Just the facts.