I am looking at a multi continent DONEWC3 ticket, basically flying in a triangle.

I am currently in Johannesburg and am heading towards Melbourne.

I was thinking of CPT-JNB-HKG-SIN-SYD-MEL-BNE-MEL-SYD-JNB, is this possible or is it too many back tracks? I do live in MEL so I HAVE to be there essentially. I thought the routing via SIN to get on the QF A380 and I would like to try and get to SYD on the way down to MEL, if I can't then so be it.

Any suggestions as well to maximise mileage?

Finally, who do I book this with? I am generally loath to use airlines as their RTW/Multi-Continent ticket staff are not always up to date with the rules, can I book it online or do I have to go with an airline? Also if I need to go with any airline are there any suggestions as to which one to book with?

What are the penalties to change the routing? Can I change dates free of charge? How long is the ticket valid for as I intend to depart and return to SA about 360 days later, final date of return is an unknown at the moment.