After I wrote my first novel (I tend to go into great detail), I read your post again. Since you already have the lifegard 300 gallon sand filter, I'd go ahead and use that. That'll save you some cash. A lot of the stuff you had listed I didn't know what it was, and some of it sounds like stuff for small tanks. Big tanks need to be done a little differently from small tanks.
For the skimmer: I like the Berlin skimmer. You can get the Berlin Turbo (it comes with pump) for about $175. It has capacity for 500 gallons. The XL turbo would be more powerful, which might be worth the extra $50 for an aggressive set-up (a lot of waste in the water). You could add the ozone later if you think you need it.
For heaters, get a couple of 250 or 300 watt heaters. It's better to use multiple heaters, so if one goes out, the other will keep the tank closer to the correct temp.
As for a sump, that is a reservoir under the tank. You drain water from the tank through an overflow into the sump, and pump it back into the tank. I think you had a pump listed that would work for that purpose. (Little Giant 2MD?) The sump gives you a place to put all your gear, like the skimmer, heaters, and the sand filter. It keeps it out of sight. I can't see not using one on a large tank like that. You can get one made at a local acrylic fabricator. Measure how big your space is under the tank, and get one that will fit.
Lighting that tank will be something to consider. If you don't have lights already, for large tanks, metal halide is the best solution. It will cost about the same as other lights initially, but bulb replacement will be a little cheaper in the long run. For a tank that big, normal output flourescents just won't give you much light, and VHO fourescents are pretty expensive too. If you get 2 or 3 175 watt Metal halides, it will light the tank and look great. In the long run, I think the MH will be cheaper. You might be able to make your own canopy and save some money, if you are handy at all. What are the dimensions of the tank? Most reef tanks suggest one light for every 2 feet of tank, but in an aggressive set-up, you can use one for every 3 feet of tank no problem. If it is an 8 foot tank, I'd plan on using 3 MH lights. The lamp you choose will really change the look of the tank. The 6500 K lamp will look like sunlight, and cost about $50 each, while the 10,000 K lamp will look much bluer or very white, and more pleasing (cost about $80-100 each). I personally do like the 6500 K lamps, and if you don't see the other lights next to it, you'll never know the difference.
For RO units, I bought the Kent MAX 60 RODI. It has a Deionization cartridge, which removes more phospates and silicates than just RO alone. You might want to get the one without the DI for your tank. Mine is for a reef, and the water quality has to be much higher than a fish-only tank. Get one that can produce at least 25 gallons per day. The 60gpd "Hi-S" RO unit is on sale at one dealer I know of for $175. The RODI Max 60 is $220 (also on sale). It would probably be worth the extra $45 for the other one. Spectrapure also makes great RO units. They are a little more expensive though.
I really believe in using live rock, as the tank will be much healthier much sooner than a tank without LR.
It sounds like you've got a long-term project on your hands!
Hope this helps,
Sonny
