Hi MREY,
I’m in Tasmania. Most restaurants will accept changes to an order so feel free to make them. Sauces, oils and dressings can be dumped on without notice, so take heed. Everywhere will usually put them on the side though.
Alice Springs has enough supermarkets that you’ll be fine. I was there 12 months ago and had no problem making my own meals. If you go to Uluru, that would be a challenge as there are very few places to eat and no shops (to speak of).
Pub meals (almost everywhere) will be your challenge, although most do steak. Fish can be a problem because it’s usually frozen and battered or crumbed.
Calorieking is an Australian calorie counter website. This might be useful.
But overall, you’ll be fine. Enjoy!