I would only use limestone or holy rock for the very bottom base rock if you went that route. You really want to get more pourus rock for the rest. You can get dried out old live rock and use it for a fraction and seed it with a good layer of live rock. This could save you some $$ if you want and it will seed pretty quick but may take longer for a good coraline to get going onto it. This is what I've done minus the limestone in all of my tanks. You can also make your own live rock, there are some good recipes out there.