Using Qantas Points to get to Europe Sept 2018 - Are there any negative points to buying a flight one at a time?

Hi, we want to go business to Europe from Perth next September, via Jordan, Rome, leave either Rome or Venice??-possibly a stop on the way home?
The 353day ahead release is coming up soon and I was wondering what do people do.
Do I wait until my final flight home is at the 353 days ahead, (end October 17), or spend the points at each release date, to ensure I get the flight day/time I want?
apart from that positive point ‘I get what I want’. Are there any negative points to buying a flight at a time? does it cost more??
Were looking at Emirates to Dubai transit to RJ to Jordan & Rome…and still undecided on the way home.

There are no benefits in terms of discounts in redeeming 2 one ways instead of a return. I would jump on it when the dates open and redeem the return flight which usually is a few weeks later, a few weeks later when the date opens.