I already know where my DD will be going to school, but that is because I am a primary school teacher and have the Luxury of knowing extra bits of information about the schools in the area we live. Like everyone else has said though, most pulic school wont take enrolments untill the end of the year before your child start kindy/prep etc. Public schools are obliged to take you if you live in their catchment area, I know some schools in Perth have closed boundaries so you have to live in the catchment area or they dont have to take you.
Dont stress about it too much, like you say lots changes in 3 years and staff turnover etc, makes a huge difference to a school.