a standard 180 gallon tank is 72x24x24. if you are unsure about fish selection, this gives you a big enough tank size to add either many smaller fish later on or a few larger ones.
In terms of rock, i prefer dry for the base as Lost said as it is mostly hidden and much less expensive. Rock these days is no where near what it was in the early 2000's. But you can still get some decent stuff off rock such as KP Aquatics. i would recommend getting rock from a few verifiable sources. I would also recommend placing in your system and ghost feeding before adding fish to help prevent any types of fish disease that may come in on the rock, specifically ICH. This can have devastating effects. It is typically referred to as a "fallow" period. Hitch hikers are common on wild rock, but most are not that bad, and a good once or twice over and a hyper salinity dip can eliminate most.
