Unfortunately leave in QR is not in addition to your days off.
We get a minimum of 8 days off per month but it is averaged over a three month period. Therefore, in the month that leave is taken the minimum days off is exceeded, this gives rostering the opportunity to give less than the minimum 8 off in subsequent months and still achieve the average.
With regard to seniority, QR has fleet and company seniority (also grade seniority). Seniority is not used for trip/days off bidding but is used for leave bidding.
So, again, if you get a fleet transfer or command upgrade you are at the bottom of the respective fleet/grade but maintain your overall company seniority.
All very complicated but that's how it is here!