1.Um, usually thats just the "polyester resin" that you also use to fiberglass. Most people here put 1-2 coats of just this on the outside of the helmet after you make it.
2. The resin that's used on the inside is the same stuff. If you've already put some of this on the outside, there's not much of a reason to put more of "just" the resin on the inside; its best to go ahead and just lay down some fiberglass on the inside.
3. Fiberglass is just fiberglass, it's jsut which of the two forms that you like. A lot of people use "Fiberglass - Cloth" because it's actually woven like a piece of cloth. Some people like to use the "Fiberglass - Mat", but its much more rugged and requires a lot more resin per coat and takes a bit of know-how to work with it as easily.
4. Sorta, if you're going to fiberglass, the Fiberglass is usually put in place, and then you paint the resin over it and let it soak through, thats the method of "fiberglassing".
Hope this clears ya up...sorry you got forgotten
~Epyon