Siren, These are good questions.
I can see you are serious and willing to learn. Here is my way to set up a reef aquarium, which will give you an operating tank within the first week.
Day 1) Mix up 25-30 gallons of salt water and aerate it by at least sloshing it around periodically. Place the heater in the largest container of saltwater and adjust the heater to maintain the temperature at about 77 over the course of day one. Find someone on this board who will give you 5-20 gallons of their tank water from a water change. Also ask them for a small piece of LR and some LS in exchange for some of your clean sand. In fact, I have some LS, LR and water I can give you for no charge/exchange.
Day 2) Place clean rinsed sand in the tank and pour in enough salt water to just cover the substrate. Stir it around slowly to get most of the air bubbles out of the substrate. Make a trough in the sand and place in it as much LS as you could obtain. Then pour in all the rest of the water and move the heater to the tank. Add the pieces of LR that you got from other tanks, which should have been kept submerged at all times, even when moving it out of the other tank. (use a bucket underwater in a method I can tell you about later)
Day 3) As soon as some algae begins to grow on the rock and/or glass, snails should be added. This may be 4-7 days depending on how much water from another tank was used and how much LS and LR was used relative to clean sand and rock. About one snail for every 2 gallons should be sufficient at this point. As Crazy Tarzan said, a variety is best, because not all snails like the same algae. Some are better on glass, some better in/on the sand, etc.
During the next five days, observe how well the snails seem to be cleaning things off and if the algae seems to be winning, add more snails.
Day 4) If you started with just a little LR (less than 8 lbs)and used a quart or more of LS and at least five gallons of water from someones reef tank, by day four you can easily add a soft coral. Watch it and see if it opens up that day or the next; when it expands and shows the tiny polyps on it's surface, then you can add another and also add a fish.
Day 5) Add the fish and coral as mentioned above. One fish we haven't mentioned is Saltwater Mollies. These are beautiful and cause absolutely no harm, ever, yet help prepare a reef tank. I can get these for free if you would like my help. I would use three or four.
(mouth unnaturally distended in this pic)
Week 2) By the end of the first week the coral and Mollies should be doing well and you can add a couple more coral, another five lbs. of LR and another fish that we forgot to tell you about, the Green Chromis Damsel. After the Mollie, this is one of the best beginner fish I can think of. It is beautiful and peaceful. If we didn't have access to Saltwater Mollies, this would be the best first fish.
Week 3) Another five lbs. of LR and 5-10 hermit crabs can be added during week three. Add more snails as they appear necessary up to a total in the tank of one per gallon.
Week 4 & beyond) Each week, small amounts of new stuff; a fish, one coral or several coral frags, or five lbs. of LR can be added. If a fish dies, wait a week before adding a replacement. Coral should not die. If it starts to look funny, quickly call one of the people you got water from and ask to place it in their tank until it looks better, then take it back.
There is more but I should stop here to let you absorb and ask questions.
Edited by Mark Peterson