It's the APS so upwards movement is dependent on staffing caps and being flexible about where you want to go. But moving sideways into new teams and areas is always an option and if you really want to get promoted it's not too difficult.
Advancement from an APS 3 at the start of the program to an APS 5 halfway through provides a better path to future promotion.
Highly variable. Depends on the branch/team. There are many opportunities for secondments etc. but not necessarily for promotion.