(You can edit your comments as far as I know.)
Shamarth explained your first question - actually I can't think of any situation where you would make the noun plural when a numeral is present. That's why I say quantity is pretty much like quality in Hungarian grammar. For the same reason, you won't use plural for the pronoun either or the predicate either. If it's singular syntactically, everything else has to be singular syntactically as well.