Salve, QS!
Apparently, the classic biography would be that from Adolph Schulten (1926?); a more recent work is Quintus Sertorius and the legacy of Sulla by Philip O. Spann, Fayetteville, the University of Arkansas press (1987). There's also Plutarch's Sertorius: a historical commentary by CF Konrad (1994).
As you may imagine, books about contemporaries (Sulla, Marius, Caesar, Pompey, etc.) or globally of the late Roman Republic (vg, The Roman Revolution by R Syme) have many references about your homonym.
Regarding primary sources, besides the obvious biography by Plutarch, please remember there is another Plutarch's book that made the comparison of Sertorius with the Greek Eumenes, multiple references in the Plutarch's biographies of Sulla, Marius, Pompey and Lucullus, and also in the respective chapters of other Greco-latin historians like Appian or Cassius Dio.
Anyway, I sugest you to take advice from the senior members of UNVR.
I hope this may be useful.
Salve Asclepiades and my gratitude! I am an idiot - I meant Plutarch when I erroneousley typed Pluto. He does rather like Quintus, doesn't he? I shall start trying to track down some of the other works though.
Thanks again
Quintus!