Thanks for the answers everyone. My goal is to buid a SYD - Europe - Asia - Europe - SYD itinary, and a separate booking Asia-SYD, as a way yo have two trips to Europe. I found a few options that works within the rules, but the stopover / connection limit in a given city is a bit of a pain to work around.
From reading your answers, it should be possible to stop in, and later connect via, a given city, which already gives me more flexibility. I ll have to keep experimenting on the Qantas website, to confirm that with segment surface, the second city is hopefully a connection, this would give more flexibility too. The example I gave before in my question was just a toy example btw.
Can I assume that if an itinery on Qantas shows 318K, but cannot be booked due to website errors, I should be able to call and book it without drama, assuming no phantom rewards were part of the trip?