Welcome to TRT!!!!
Ah I am very familiar with that tank - it was my first horribly failed sw tank
BUT you came to TRT FIRST, so you have a much better chance at success than I did!
Question 1. Um yes you CAN have a 5 gallon saltwater tank.
Question 2. What do you need
a. PATIENCE
b. MORE PATIENCE
c. research - I know your in college, really who wants to study, but with a small water volume you have less time to correct mistakes, so the more you know... well yeah you get the idea.
4. you will need - saltwater - you can make it yourself or see if you can purchase from your local fish store ( LFS). To make water you need, something to mix it in, a power head to mix it, a heater, and a refractometer to measure the specific gravity - you can use a hydrometer, but they are not as accurate.
5. you need live rock - can be bought on the internet, from local reefers with extra or your LFS
6. You need substrate - a fine sugar type sand is usually reccomended
7. heater
possibly an auto top off ( ATO) this would keep your salt content more level.
8. later on - clean up crew ( snails, hermits)
9. fish
10.coral
debatable.....
Others have mentioned a different light... with the shape of that tank that might be hard to do. Let's see what others have to offer.
If you can fit a compact flourecent light bulb in there you may be ablt to keep some low light corals - but remember you don't have that much room. search zooathinds, mushrooms, and leathers that's a good basic place to start.
There are plenty of very fun small invertabrates that you can keep- look into shrimp - I am a fan of the sexy shrimp which would be oh so cool in a 5 gallon tank.
fish - think blenny or clown gobie, or watchman gobie and pistol shrimp pair... 5 gallons is really not a lot of swimming room for a saltwater fish, esp since it is more of a taller than wide tank. Those are some of the fish I would look into and I would honostly only put 1 in.
question 3.
research research reasearch to make sure you really willing to do this. It's not so much that it is hard, as that it takes detication. THe more you add the more time it takes.
Fish only that would be least time intensive
fish and inverts ( shirmp, crabs, snails) a little more time
add coral to that and you are adding more time
the choice is yours and we will do our best to help you with what you decide!
Keep us posted!