According to gcm your itinerary is just over 34,000 miles
But that can be easily fixed - for example just reverse the order of SYD and MEL
Other than that, your itinerary appears valid to me.
Other thoughts:
- unless you want to go there, there is no requirement to return to JNB - anywhere in Africa will do (Africa as defined in the rules, in other words excluding North Africa); having the final segment to somewhere in West Africa would free up a lot of miles to use elsewhere
- You are using only 13 of your allowed 16 segments; however it appears you are using your allowed maximum of 4 stopovers in each continent (other than Africa)
- Perhaps you could fit in some stopovers in Asia or even Nth America