There is only a single place to get coldwater marine livestock I'm aware of and that is
http://www.coldwatermarineaquatics.com . The owners Stu and Josh are based out of Portland, Oregon and do lots of collecting off the coast of Oregon but also bring in livestock from Japan, Southern Australia, and the UK. They're a pleasure to buy livestock from, can't say enough good things about them.
I run my tank at 56, which my chiller keeps from 55-57. A thick acrylic tank helps (mine is 1/2 in but others consistently have 3/4 to 1in) insulate quite a bit. I do have some condensation on some of my reactors right now due to a bit of a heat wave here in Tacoma, WA. Good airflow clears this up.
As far as running the system, it's more akin to running a heavily stocked fish only system. You have to process a lot of waste, and because of the rock used (non porous relative to carbonate reef rock) and the lower temperatures, biological filtration moves at a much slower pace. On this system I have a large skimmer, a biopellet reactor, and another reactor running RowaPhos. I dose vodka daily and I do about a 15% water change weekly with natural seawater I collect from puget sound. With all of the filtration, I can't keep my nitrates below 30ppm which is similar to the experience of Stu and Josh and coldwatermarineaquatics. The plus-side, evaporation is next to nothing and there's no need to worry about calcium additions because there isn't a high demand in the tank. I do top off with kalkwasser to bump up the pH a bit but the additions are so infrequent, the effects are probably negligible.
I have an automatic feeder using a dosing pump and a refrigerator which helps keep a constant flow of small food items to the tank. Despite the automatic feeder I often spot feed anemones every day or two.