Just a thought on Tassie. You might already know we adore the place (and are going back in a few weeks). It is way bigger and slower than you think. 4 days is enough to do perhaps Hobart (if you want another nice small city experience) and one park (Freycinet or Cradle or ?). Or replace your undecided time, Uluru time or extra Sydney with Tassie. Then you might be able to do two parks and Hobart. Check and out, and definitely go - you won't be sorry.