I don't know how common the squirrel is in the furry world, but it's a great choice since squirrels are so common and easy for anyone to identify with.
And honestly ... the more I think about, the more the idea of a furry serial killer really could start a "genre". Vampires/werewolf mythos has been around forever, but even more so these days with Twilight being in the mind of every teenager who sleeps and eats. Equating a "real life animal-other-life" with the drama/gore/shock of serial killing and you've got yourself a half a million newbies, goths, and emo's willing to seek out the furry lifestyle and take it to the next level, in some ways that is (and obviously I'm not insinuating they start suffocating people for kicks and stalking their romantic interests as furrys

)
I think a fascinating poll would be to find out how many people are actually attracted to individuals who have alter personas in regards to animals. In some ways, it's really no different than being attracted to the charisma of an actor/actress who plays a role ...
Dude Ryan Reynolds is fantastic in every role he's cast in imo. I might be overstating his talent, but in some ways I think he's a white Will Smith (minus the musical talent). He has an ability to convey complete asinine behavior one moment, and then come off as a serious human being the next that you actually feel for.
And if you're serious about Rowdy Roddy Piper ... I wouldn't make him Brad (although who am I to give armchair advice? LOL) He could be Stranger if Stranger is going to be an older, more seasoned psychopath that essentially mentors Brad into his murderous behavior. Since Piper echoes back to the totally-freaking-awesome
They Live cult classic, he should be the psycho-father figure. Starting off somewhat naive and then becoming more keen to his psychopathy later as Brad seems out of place for him, imo. He already knows the world is crazy since he donned those glasses so many years ago so let him show what those years have done to him LOL
Now, I'll tell you who I think would be great in one of the roles .... in all seriousness .... Dax Shepherd. I wonder how "expensive" he is?
Now don't forget that the Jonas Brothers need to get hacked by a 7 foot squirrel