size wise and working id probably suggest some of the terriers...if you want to go a little bigger theres some in the hearding class that woudl work too...native austrailan breeds would work wonderfully, there bred for the land and temperatures, a little larger than you wanted would be australian cattle dog, or aussie shepard...these are working driven dogs who will readily leanr any aspect of farm work...
the cattle dog is very loyal but always ready to work, strong protective and never afraid, Aussie shep is more into hearding than protecting and prefers faster paced work.
if you want to definatly stay on the smaller end theres a few terriers that would suit a working lifestyle look into the australian terrier which would be a great choice for you living down there...boarder and cairn terriers, norfolk and norwich terriers, jrt(or parsons russle terriers), and the veriety of fox terriers...these dogs will also be happy to work and are pretty much low maintenence coat wise... ANY dog can have a reliable recall so long as you train them to! you should NOT be letting any dog whos not got a good recall offleash...this is all part of the puppy training, and NO dog comes to you as a natural behaviour when theres something more important going on...ALL dogs must be trained to recall before theyll come...jrt's are no more difficult to train than any other breed...
hope this gives you some ideas of breeds to look into...