Yeah, there is no info on what mods you are after. Body? Paint? Engine? Suspension/brakes? Oz doesn't really have many places that are one stop shops
Best to figure out what you need/want then start asking questions. If you don't know, educate yourself first, modding for the sake of modding is a path to fail
Re: Tunehouse, my bro had work done by them, no issues, except price. But, a mate with who blew a motor built by Tunehouse, due to a bad tune, got shafted by them, so tread carefully
If you are on a budget and want power, try Billtech in Sefton/Regents Park. Some big power RB25's coming from them lately. I also like Advance Motor Mechanics in Strathfield for all the stuff I cant do on my own