This is what I am doing with my 180. Most of the fish found on the GBR are found throughout the Coral Sea area (Solomon Islands, New Caledonia, Vanuatu, Fiji, ect.) with a few fish like the personifer angel being endemic to the GBR. What kind of setup is it going to be, FO, reef, mixed reef, SPS? What kinds of fish are you interested in? Fishbase will give you the geographic ranges of fish you might be interested in.