Trying to get my head around this and reading all the guides. I have 438k Velocity points ready to redeem for my first business class flight! One of the guides said I can book Brisbane to Singapore to Frankfurt, spend time there then fly on to Athens with Star Alliance and return the same way? Can I do this as one return ticket but come back through another city such as Munich -Singapore-Brisbane? Or would that mean two bookings and more miles? I just want to take advantage of as many cities as possible.
Thank you 
Adding the athens leg means you’ll move from the Krisflyer award chart, to the Star Alliance / partner award chart (with higher rates / taxes etc). If you have points / $ spare then this isnt an issue. If you want to stick with the cheaper chart but experience as many cities as possible, you could look at the singapore routes with stopovers (eg. SING - MOSCOW - STOCKHOLM).
The guides are correct - you get some free stopovers (depending on ticket type) after which you pay $100 to add more.
Returning via a different route isnt an issue though - the charts price for one way.