Welcome to the boards and the hobby! :happyfish
The water you have is most likely RO/DI water; short for Reverse Osmosis Deionized water; the best kind of water to have.
Hydrometers, unfortunately, are found to be somewhat inaccurate. Depending on what creatures you plan on having in your tank, the salinity of the water is very very important. If you could spare the money now or sometime in the future, I highly recommend investing in a refractometer. If you're unsure of what one is, this website sells them in the Dry Goods section.
Most people on this board have their temperatures set somewhere between 78-83 degrees fahrenheit. As long as it's somewhere around 80, I'd say you're good to go. I keep mine at roughly 80; it usually raises about a degree when the lights are on.
I would get the live rock now. It will help to cycle your tank. I would also recommend getting all the live rock that you're planning on having now; this way, you can avoid the hassle of curing rock before adding it to an already established tank (adding uncured rock can cause your tank to undergo another cycle; something that can be fatal to any inhabitants). You could still add rock later; it just might be a bit more of a hassle. Also, concerning the cycle of your tank, I recommend cycling with a couple cocktail shrimp from your grocery store. Cycling with fish is not a good idea, no matter what any local fish store (LFS) may tell you!
You don't want to leave your lights on all the time. A common time frame for lights is to leave them on for 12 hours. However, this has caused algae problems for some. I think you'd be alright leaving them on anywhere from 8-12 hours a day. A little more than that wouldn't hurt, either. Another item you may want to consider is a timer for your lights. Having the fish on a consistent lighting schedule is a definite plus for them. I myself don't have a timer yet...but that is something I plan on getting as soon as I get some money.
Hope this helps! Feel free to ask anymore questions you may have.
-lefty
