the single ply would be best unless your stupidly front heavy.
about the comps, when you get there you sign in, you get a card and you go to a section. when you at your section just give your cards in to the observer and wait for your name to be called out, its as simple as that.
if you have a mate going who knows his way around go with him. my first time i hadnt a clue what i was doing but i went round with some mates.