score:5
Since you're connecting Qantas to Qantas, you're entitled to use the free Qantas transfer service. Basically:
And yes, if Qantas sold you connecting tickets, 90 minutes is sufficient, although only barely (IIRC that's the minimum allowed). You should be OK if your flights are on time, but even if it comes in late, Qantas will put you on the next flight -- although for SCL, that might mean waiting a day.