Ha! There's a good chance I may have crossed paths with your dad then. I wasn't in Exmouth, I was in Kununurra and Broome in the early 90's.
Staying in Melbourne, Pros. It's with your friends and family and all that a big city has to offer. Cons. You can get "stuck" with instructing and whilst it's not a bad career path, there's fierce competition for what little twin flying there is. Also, you have to find your own students etc and the Instructor rating is not cheap. You will not earn a lot of money. (Come to think of it, you won't until you make it to the bigger regionals/mainline)
Heading up north. Check out the Dununda forum for more info. Cons. You're away from home and you need to be able to cope with that. If you're used to a pretty comfortable life, then sharing a house with a bunch of blokes may be a bit of an eye opener. Competition is very fierce for any job. You'll need to do any work to survive. Pros. If you're persistent, flexible and not an idiot, someone should take you on. You'll be doing charters/scenics etc in some of the most remote and beautiful places in the world. Twin progression should happen quicker. You'll make contacts and friends who'll really help for the next steps in getting turbine jobs etc.
About that 5 years. It's a guess. No one really knows. And if for some reason you miss out on QF, what then? It's great to have a goal but you do need to be pragmatic and flexible.