[justinl]

If you do a coldwater tank, the key is knowing where your inhabitants live in the wild and what they're exposed to. Go talk to public aquarium staff for suggestions. I highly discourage just setting up a tropical tank without a heater. I really think a chiller is mandatory, not optional. in the end, a CW tank should cost less than an SPS tank... about the same as an LPS tank probably.

random tips:
-skip intertidal photosynthetic organisms like nems and algae. They need lots of light (halides).
-stick to "other" intertidal animals for ease of collection. Stuff from the intertidal will also be a lot hardier.
-know what you're collecting. that rock prickleback may look cute at a mere few inches, but when it's two feet long and has eaten all your other fish, you'll start to have regrets. same goes for inverts. i suggest bringing an ID book or a knowledgeable friend (both would be ideal) with you when collecting.
- on a related note, no filter feeders. mussels, clams, barnacles, crinoids will not do well without daily target feedings.
-most of the local stars are heavy carnivores that require target feedings of clams (which is easy), not detritivores. some of them can be a danger to fish. again, just know what you're collecting.
-don't break laws. you can't collect some stuff, and i suggest you get a permit when you do this... i believe most places require nothing more than a fishing permit.
-if you want exotic CW animals, steve weast (on RC) knows some international suppliers.
-think about the cold water. your glass tank will sweat. you can ignore that (it isn't vital), or splurge on an acrylic tank. Ive also wondered about trying a zero edge CW tank... or trying a DIY zero edge. how much it will sweat really depends on the humidity in the place you put the tank.
-VITAL: remember that at cold temps, the nitrogen cycle will slow to a crawl. don't even bother with filtration that depends on it. even LR will lose it's efficiency in this regard. you have to get the crap out before it decomposes. low stocking (low bioload), huge sump (volume), big skimmer, frequent water changes, etc are good ways to deal with this.
-things you can skimp on: lights (just aesthetics... a single bulb T5 strip would be fine imo), any reactors (no need at all).
-things you should splurge on: skimmer, chiller.