hi there. good to see ur on board. nice car, i was going to go for an xe fairmont ghia myself, with a 302C and slightly, um, well not so slightly :), work it.
Im guessin u have a 6 seing as its 83 and coz its fairmont ghia its EFI right??
Well first off a nice set of headers with real, real long primaries will be sweet into a 2.5" system. Will flow great and sound awesome. Also install a k&n airfilter to allow inlet air to flow better. While ur at it get the injectors cleaned to by a professional.
How much money to u want to spend on the head unit?? about 300-400 will get u a real nice one from JB HiFi that has everything u'll need and some even have Dual RCA's (so u can hook up a heap of amps later down the track without having to split the signal from on one set of rca's)
whereabouts in melbourne are u? most suspension places such as the tyre factory are quite good.
cheap resprays, well, all im gonna say is that u get what u pay for, and a cheap respray is exactly that, cheap. paint is often only a few costs thick. it can look shaby within a year.
i forget what the dash for the stereo looks like? was it sort of more of a square than a rectangle for the original?? even if it is, just sand some of the plastic away and use an instalation harness and the deck will sit in there sweet.