I personally would suggest just redeeming your Qantas Points outright for the whole fare.
Upgrades are not guaranteed. Your plane might end up super full and thus you miss out on the upgrade. If you want a guaranteed seat in Business Class, outright buying the ticket with points is the best way to do it.
I believe the schedule opens 297 days from departure for Bronze and Silver members. 297 days out from when you’d like to depart, check the situation and see how many seats are available. If there are seats outright for redemption with points, book them. If there aren’t, you may decide to play the waiting game or buy a paid ticket then upgrade.
Keep in mind though that certain types of paid tickets like ‘Sale’ fares are not eligible for upgrades.