You are correct if you are thinking about 'you' in the (informal) case; e.g. someone you know well, a friend. Although I'm unfamiliar with the verb, if it follows convention then you (formal) would take on the same conjugation as he / she / it (informal). Of course without the article, and without context we cannot tell which.
rules for imperative for interested readers. http://italian.about.com/library/weekly/aa011900a.htm
Right. Triple and double negatives are common in Italian. Perusing the patterns on this site can be helpful:
"Niente" Means "Nothing", However Unlike In English, Having Two Negatives Doesn't Negate The Negative, But Instead Reinforces It, I Believe, So While "Non Indica Niente" Literally Means "He/She/It Doesn't Indicate Nothing", That's Unlikely To Be Used Unless You're Texan, As It'd Mean That He/She/It Does Indeed Indicate Something.