If you have trouble finding them local, but can't wait for shipping, try a car radio shop. They should carry the smaller connectors for speakers.
Wire to handle more than your transformers max output, and fuse at slightly less. Breakers are more to protect the transformer, they are not really meant to protect the track though they do in a way.
Wire gauge needed is also based on wire length. Longer must be thicker at the same volt/amps.
I go with 12g and never worry much if something it feeds goes "poof".
