If I were massacreing them, I would go around shooting fireballs everywhere, probably screaming things, and killing guards.
Ah, I've done that before, just gone around systematically obliterating each town. It was good for killing boredom too.
Something like this, I say do a little of everything, see how creative you can get with waiting for the opportune moment and method. Poisoned apples in the beggars' bags, that's a good way.
And since you're Khajiit and already started, maybe save Leyawiin and/or Borderwatch for last.
Does kitty feel a need for revenge? Or is kitty just crazy? Khajiit can have some motives that don't quite jive with the humans and mer -- perhaps your Khajiit is an escaped slave from Vvardenfell, bent on the decimation of those who might have been his former captors?
Also, no matter what your reason is, it'll probably be so diluted by the time you reach Bravil that entering the Isles to continue your "cause" would make complete sense. To the character that is, not to you, by then you might find that you've created a monster.