We are also in QLD, with baby #4 due around the same time... I had babies born in March, Nov & June...
Sheets I would say 2 cotton & 2 flannel as a minimum, maybe another couple of sets of cotton? If all is going well you only need one on the bed & one in the wash, but if Bub is sick or starting to wet through nappies etc you will go through more.
As for blankets I have 2 comforter/quilt type things - but lighter blankets are better, you don't want bub to get too hot. I used to use 1 or 2 light blankets & rely more on dressing them warmly. Bunny rugs are good. QLD winters aren't too long or cold, also if you have wriggly babies they will kick them off anyway.