C'mon, give me a half-point at least.
It's a tough language.
-as indicates a 2nd person verb. "You ...". You are nothing would be "tú eres nada"
"You are nothing" would actually need to be "Tú no eres nada." You need the "no" in front of the verb as well.
No, it wouldn't. You're applying English grammar rules to Spanish, and they just don't fit.
In a negative Spanish sentence, there must be a negative word before the main verb. If a negative word like nada, nunca, or nadie comes AFTER the verb in a Spanish sentence, you must put no before the verb as well. If the negative word comes BEFORE the verb, you don't need no.
And Spanish has no rule against double (or triple, or even quadruple) negatives.