Welcome, Fly.
The experts will come along in due course but in the meantime . . .
1. Yes, an e-ticket will result as soon as you make a booking. You have the ability to change but of there is a cost. From 1 December this will be 5k each time you change plus a fee of approximately $80.
2. I'm not too sure what you're asking here, sorry.
3. Yes, the call centre is most likely to be the best avenue and charges for doing so may apply.
4. Are you asking the earliest point at which you can finalise an itinerary? If so, the earlier the better. If you're asking how late before you start travel can you make final changes, I believe you can go almost right up until departure but I would not leave it less than 24 hours. I believe there is a rule that once travel begins you are not able to make any routing changes (although you presumably can change dates and time - naturally, for a fee).
5. Because you're using QFF points the availability of award seats that Qantas has will determine what is available to you. That is to say that award availability is often not equal across oneworld carriers. While AA might show availability on a CX flight between the US and HKG, Qantas won't be able to see it and therefore won't be able to sell it to you. The Qantas engine, however, doesn't show availability for all oneworld airlines. For example, award seats on Malaysia Airlines can only be determined by phoning Qantas. Alternatively, some other oneworld programs do show others airlines. For example, BA does show MH availability online. Meanwhile, ExpertFlyer doesn't show award availability for a lot of others, including CX. This is the reason some people suggest using other programs.