All of the male characters (except two) are named after characters portrayed by the actor Nathan Fillion, who writer/director James A. Ward happens to be a big fan of.
All of the female characters are named after characters portrayed by actress Jessica Harper, who writer/director James A. Ward is a big fan. The name of The Hit Girl herself, "Jessica", comes from his admiration of Jessica Harper.
Writers James Ward and Robert Bruce came up with the idea for The Hit Girl back in 1991 and have been talking about the project since that time. The original character concept for the "Hit Man" was based off of their mutual friend James Williams, who was a former marine, strip club bouncer and total badass. The idea of him somehow being turned into a little girl, but still acting being a badass was the inspiration for the movie. He appears in the movie as Bruno and has a fight scene with Jessica.
James Ward meet the band members of Adam West the Bat, who's music appears in the film, while attending Wonder Con in Anaheim. Adam West the Bat shares the same bass player with The Green Lady Killers, so James got to later meet with them, and their music is also featured in The Hit Girl.
Patrick Beckstead is (and hopefully always will be) killed off in all of James Ward's films. In Identity Theft he is the Wounded Man at the beginning of the movie who dies after the body thief steals the doctor's body, In Glinda Gone Wild he is the Scarecrow who is burned to death and in The Hit Girl he is the warehouse thug who talks about 'Jimmy the Nose' just before Jessica shoots him.