zombie apocolypse one-shot

Thinking about doing a one-shot for Halloween at my FLGS.  What level should I have the players make and how big/small should i make the campaign?

My first thought was to a survival mode campaign but then it leaves a lot of people sitting while the others play.

My second thought was a cursed town mystery, with dead pcs being npc controllers.

I'm partial to a mixture of the two but I'm unsure how to keep it interesting...maybe something a la Zombieland....

Thoughts?

I'd say level 3 or level 5 depending on how dangerous you want the game to be.