"Are the streets new?"
Translation:Jsou ty ulice nové?
The word nový (nové) is a part of the predicate (jsou nové) in the sentence (Jsou ty ulice nové?), while in your suggestion (nové ulice) it develops the noun ulice.
Yes, that's right. In the nominative. :-) Just notice that the "i" is short - ulice.
You have to use it, because the sentence refers to particular streets and saying that those are new (ty ulice - the/those streets).