Wooo great advice here, thanks again.
I could do some simulations testing the stopover / connection scenarios, looks good. I could find some
A->B - stopover in B
B->C - stopover in C.
C->B - (Surface segment)
B->A
I took some screenshots. At least, this fills me with confidence I could make my case with an agent without sounding uncertain if needed. Of course, the outcome would depend who is on the other side of the call.
I also got to understand the reason of the many error code at the end of the booking in my case. I was actually searching flights departing from and returning to CBR, and those search almost always failed for me (maybe too many segments in total?). Departing and returning from SYD looks much better in my simulations.
This brings me to my last set of questions before I pull the trigger:
1. I understood it's easy to call and add some segments after the booking (i.e. add a CBR-SYD and a SYD-CBR), right? How about more advanced rebooking requirements that I might need to do. For example, my trip is essentially composed of two half trips, but if later I need to move the first half after the second half, doable, assuming availabilities?
2. What happens to points and cash if after half of the trip, I would need to cancel the second half?
3. Did I understood correctly that it's ok to start and book the trip now, and add segments as seats are released by airlines?