Commentary

• cum ... putaretur: Since, over the course of four years, Sertorius had garnered such strength throughout the entire Iberian peninsula, the Senate was fearful of the rise of a "Second Hannibal."
  
  Translate as "since Metellus alone was thought (to be) ..." CumCaus
• fortuna varia: He fought "with varied fortune." AblMan
Octavo demum anno: As the war wore on, his Spanish allies began to tire, and it was rumored that Sertorius, known for his kindness, was becoming more cruel. His ally, Perperna, turned against him and killed him in 72BC. Demum is used to separate octavo and anno. AblTime
per suos: Supply milites.
datus ... redactae There is an implied est with datus and sunt with redactae.
per Cn. Pompeium: Remember that Eutropius uses per with an accusative to show agency.
in dicionem populi Romani: Under the Lex Gellia-Cornelia, citizenship was given to many Spaniards, who had supported the Romans. Much of Spain was placed under Roman rule.