Originally Posted by
GlobalSTL
although when you purchase SYD to GUM on CO it does allow for a QF flight to CNS.
No. Also keep in mind that the CNS-GUM flight is not daily.
To your other questions, you should be able to do a stopover in GUM and then continue on to any of the other islands as your "destination" on the single ticket, since GUM is on the most direct routing. As for when to visit and where to go, that depends a lot on what you're looking to do.
S.