if it was me I would go native marine! It would not be much more difficult than a freshwater tank and the additional costs would be negligble in terms of the costs you would be talking to fully plant out a tank this size. The only extras would be a nice big DIY Skimmer and feeder pumps, a big watter barrell and trailer to pump NSW and a chiller. If you kept it in a well situated place with plenty of insulation it would probably cost less annually than heating a tropical tank... and finally, all the rocks, kina, fish, starfish, anemones, crabs etc are all FREE!!!
althouh 2000 Cardinals would look nice too!