We had a rock pool marine running for a couple of years and it was the most interesting tank we've ever had. We had to give it up though as we did not have a chiller and the tank kept getting too hot.
All we did was take some containers down the Kaikoura coast and gather up rocks and sea water. We also caught as many critters from the pools as we could, brought them all home and put them in a 3ft tank. This tank had an AquaClear running off it and no other equipment.
Critters in there were anemones (prised gently off rocks with flat edged knife - or try to get a small rock with anemones on it so you can take rock and anemone), chitons, triplefins, rockfish, hermit crab, starfish, cushionstars, brittlestars, shrimps, sea cucumbers and, at one point, an octopus.
Critters were fed sea lettuce every now and then but nothing else. Lots of microscopic stuff would come in on the lettuce. Seaweed won't live. Nothing died and the shrimps reproduced.
Since there is no coral in that region, our tank didn't have any. Live rock isn't necessary in a rock pool either.
We never had a skimmer, powerheads or any other equipment and it was never required. I imagine there will be a difference in the needs of a reef compared to a rockpool though.
As far as the law goes, I believe it is illegal to collect undersized paua and crayfish and a lot of the bigger marine fish but anything else in a rockpool is fair game.