The traffic police in Melbourne arent something you want to become too familiar with. Theres also the fairly strict rules about what you can and cant do as far as modifications go. Its been a while since I got a car registered in QLD, but I remember having no trouble getting a RWC with bald tires etc.
Anyway, as far as employment in this kind of area, try doing it part time intially, or just one offs. Its not exactly a high demand job. With some pictures of previous work, youll find it a lot easier to get new work. The other option is getting into a similar industry that does custom fab on the side. Youll be able to use your skills in a more steady line of work, while still being able to be creative from time to time as custom work comes up.