Nāsōnis
This is Ovid's cognomen in the genitive

Nāsōnis
This is Ovid's cognomen in the genitive

lēgisse
This is a perfect infinitive from lego, legere legi lectum. It it functioning here as the subject of sit "To have read us would be..."
Arma gravī numerō violentaque bella parābam
This is an allusion to the Aeneid