DONEx prices are flat fares depending on the number of continents visited (with supplements for additional sectors within a continent). They are already deeply discounted as against buying the sectors you want one by one, and as such they do not go on "sale" as such. They are, however, priced wildly differently depending on where your ticket originates, and under some circumstances, where it is sold.

I would be very surprised if BA honoured the A$1000 off voucher you mention for a DONEx. For it to apply, you would need to have the booking originate from Australia so that it would price in AUD, and also ticketed by BA. And even then the conditions may say it's only valid for normal roundtrip bookings.

I'm not familiar enough with QFFF rules to know whether they'll allow RTW bookings using points.

Hope that helps somewhat.