Unfortunately, yes. Book as soon as you can see the seats. For that reason it's not at all uncommon for the 140k/280k/420k to cost significantly more once changes are taken into account.
From memory, Qatar uses married segment logic which means while you may find MLE-DOH, for example, you may not find MLE-xDOH-CDG. But, again, book when it comes available. The upside with HEL-SYD is that there are a number of options other than via DOH so if points are an issue, you may consider holding off booking that one until all the flights you need are available. You also have a tonne of miles up your sleeve (as in the maximum number of miles you can fly on this award) and as you're flying in J I'd absolutely be looking to maximise that.