sounds like cyano. physically remove it. read this http://www.netpets.org/fish/reference/r ... teria.html
yes and no. since its reasonably small, if you keep up with regular water changes you should be right. a decent skimmer will make life that much easier between changes by pulling out the crap you add (in the most basic sense)
yes, any (half-decent) skimmer will help. pm steve for info on how to mod it to fit a skimmer.
as you are mushrooms, leathers, all those types of corals that are both hardy and have lowish light requirements. most soft corals.
anything is possible. again, ask steve he's modd'ed them so will show you how. for a small tank like yours a single 150W halide should fit nicely. the typical 150 you can get has a small footprint that might squeeze in nicely.
there is heaps to learn but but top marks for giving it a go at your age. good luck, keep reading