Hi Kasey. We had a cold water marine running for almost 2 years and loved it. We had a 3ft tank with an AquaClear filter hanging off one end and nothing else. We went down the Kaikoura coast with large barrels and gathered some sand, rocks and water. We gathered critters from the rockpools including; anemones, shrimps, brittlestars, starfish (7 armed, biscuit, common cushion and comb) rockfish, triplefins, crabs (including different sized shells for the hermit crab), chitons, sea cucumber and an octopus someone caught in their fishing net. Paua did not last as we could not get the tank cool enough and didn't have a chiller - a necessity.
Our only problem was the heat. With the room sitting at 28C it needed to be around 15C or less (pref 10C) for the inhabitants to be comfortable. Although rock pools reach high temperatures, it is for short periods only and they do not handle constant warmth.
All we ever did was top the water up when it evaporated and occasionally added more sea water as a way to introduce microscopic greeblies as food. We also added sea lettuce as food but otherwise didn't feed the inhabitants.
Good luck with the tank, it will attract a lot of interest.