I am also in Victoria (Melbourne based but do travel) and can help you if you need. From what I have read on this forum, Nehkbet is also good at what she does and will help you if you take this option.
Most problems start in the house. You need to game control when at home first an extend to outside when you are confident. If you are not confident, your dog will rea this and respond accordingly.
I'd definitely be getting a muzzle for walking and I also look into getting a different lead to ensure no rope burn occurs again. Poly-cotton is great. It will also benefit you to learn how to hold the lea correctly to prevent lead drops. Others may have their ways but I put my thumb through the loop and then clasp my remaining fingers over both sides of the handle so your thumb is locked in. Hold it like this and then try to pull/yank it out with your other hand to see if you are holding it correctly. It should be nice an secure
It sounds like your heeler has either had some negative experiences with some small fluffies or it feels anxious on walks and needs to "protect you" when out and about with any dog, given that is reacts to dogs it sees regularly out in te walk. The fact that your dog is running up to the other dogs and attacking is a concern as it is choosing to fight over the other two options - flight or freeze/avoid. This will need to be modified.
Please also feel free to contact me if you would like more information. - firstname.lastname@example.org
I'm sure at least one person in Victoria will be able to help you. Nehkbet has been around the industry for longer than I have and will help you if you contact her.
Good Luck and keep us updated.