I hope this isn't too overpowered - I mean, being able to disguise as someone and instantly kill would be a bit OP if he had loads of health - Maybe server prefs of some sort to define health per player?
(Like how Vs saxton hale's health works, it has a base health that increases by X with each player)
So you could have a 100 health thing that truly encourages stealth, or a 1000 health one for a massive bloodbath.