My first saltwater tank 20 gal.

Hi All,
So this will be my first saltwater tank ever. It all started when I was going to get a small desktop tank for my desk at work, as one of my coworkers has a beautiful fluval edge with freshwater fish in it. However, when I started reading I stumbled across some saltwater information and got hooked, and now I can't stop reading, watching videos and loitering in fish stores. I really wanted my first tank to be bigger than the 20 gallon one I'm starting with, but alas I live in a condo and I may move in a few months to a house (maybe go big when I have a house), meaning this tank is not for my desk at work. Anyways here's what I got so far, along with some advice requests:

Setup so far:
20L gallon glass tank (30'' x 12'' x 13'')
A 30" fixture with a 24" 17 watt 8,000K Full Spectrum fluorescent lamp
Aquaclear 50 hang on back filter (has a sponge, carbon filter bag, and wet/dry biomedia)
Fluval 100 watt heater (the stick style with suction cups)
About 1cm of a white sand/crushed coral medium on the bottom of the tank (from "The Fish Store")
About 15 gallons of saltwater at 1.025 specific gravity at 75.5 degrees fahrenheit (to leave room for live rock)
A tiny little powerhead that's kind of ugly and makes more noise than I would like (from "The Fish Store"). Thinking I'll get something better and use the noisy one for mixing saltwater solution.
Wonderful little digital thermometer by Marina (from "The Fish Store")
2 young cats who are convinced they want to go swimming, and probably fishing at some point.

Questions:
I was told by a gentlemen at "The Fish Store" that I don't need an RODI unit as Seattle water is fairly clean. Instead he sold me a bag of saltwater mixture that had "The Little Bottle that Makes all the difference". Do I need an RODI unit or some sort of water treatment formula?
Should I test for chlorine every time I do a mix?
I was also told at the same place that on a tank this size to just "Fill it" with live rock (1-2 pounds per gallon), and that will be your biological filter handling all the nitrates. Is this a good approach? Are there better approaches? Just want to make sure they weren't just trying to sell me $200-300 dollars of live rock.
Where's a good place to buy live rock, maybe at a better price than 7-10 dollars a pound? I don't want to sacrifice on quality of course.
I was told my lighting would be adequate enough for anenomes (like bubble tips), live rock, and maybe some soft corals (like mushroom), is this true? I know what I have is simple and cheap; I just got it to keep the cats out.

Notes:
While I'm trying to not spend a fortune, money really isn't an issue. I plan on going all out when I get my big tank later this year, which is why I didn't want to dump a whole bunch of money into this little setup.
I think nudibranchs are the coolest thing ever, I'd like to have one or three of those someday.

I still have some serious gaps in my education and obviously I've just starting getting my hands wet. Any answers, advice, criticism (be gentle I'm doing my best), and/or critiques are most welcome.

Get the RODI. With saltwater, you want to remove *everything* and then add back in just what you want, in the quantities you want it.

Lots of live rock is usually a good thing. But you want to have an aquascape that pleases you.

Personally, if I were setting up a saltwater tank, I'd be heading down to Barrier Reef in Renton.

you can find live rocks on craigslist, avg $3 per lb
and get a HOB (hang on back) protien skimmer.

I learned that the hard way not getting the protien skimmer.

I hear that some spectrometer is not accurate. Getting a refractometer would be more accurate. Salinity rate 1.021 to 1.026 is good, anything over would burn thier gills.

I am using tap water to mix my salt, no RODI unless you want to do reef.

I started mine last Novemeber.

Hey Thanks.

larry.beck - Barrier Reef looks like a paradise of a store, I'll check it out as soon as I can. As far as RODI units go, does it matter if I get it at home depot or are the aquarium specific ones special?

gobluecichlids - Craigslist and the forums here look like a good resource for live rock, good idea. Think I'll establish a good cleanup crew and plenty of live rock before I get a skimmer, mostly because I don't want tons of stuff hanging off my tank if I can help it. Plus, the tank is not really in direct sunlight. I'll watch the algae and nitrate levels like a hawk though.

If you get RODI unit, get a new one on ebay (I got that from a salt expert)

I was advised not to get a used one, since you'd have to replace some that would just cost you what you would pay new

I'm still considering getting one someday...

You can also buy RODI fresh water at some stores like Barrier Reef or Blue Sierra for something like .50 a gallon. I do that for my 28 gallon nano tank, pick up 5 gallons a week, mix up the salt water at home and change out 5 gallons and have a little left over for top off.

for saltwater you got to use RO water. if dont hair algea will grow like crazy. Get a much live rocks as you can, thats your best filter source. this is the RODI unit that i'm using.

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My tank just finished cycling with 11 pounds of Fiji live rock. I think I'd like to get more live rock, but I also really badly want to put something more alive in my tank

Thanks jamestosa, I picked up the same RODI unit off of ebay. It's rather impressive, and now if the apocalypse comes I can have clean water.

Also, larry.beck I went to Barrier Reef and ended up walking out with a glass 4G nano tank for my desk at work and ordered a 30 inch T5 2 fixture setup. What a beautiful store and totally worth the drive.

I visited barrier reef last month, very nice and extremely clean tanks..I got a chance to to see some nice fishes. The blueface angel looks cool.

Red C aquarium near Mountlake is really nice, he just opened for business last summer and working on a freshwater section.

Hey, its been a while. Would like to see some pics of your system.

Yeah pics pics pics