I would say, if someone is considering a 500G system, the cost is not an issue.
Size really depends on what you want to accomplish.
If I had space and the means to support a 500G tank..... Heck!
BUT as mentioned.... exponentially more for everything. From salt to lighting to rock and sand... coral and fish. You will have an empty 500G tank with 3 frags and a blenny, if you know what I mean.
Be sure to start a build.
