Okay, first off check ebay and google for "Not Yet Dead" and look for 54mm models. There are a number of zombies available that could be used as is or with conversion.
Next up, Karloth:
He'll probably have the Puppet Master, Scan, or Detect, or Mind Scan skills, and maybe one or two other telepathic skills.
RAW He'd probably have both Force of Will and Nerves of Steel (normally unlikely as most 'clavers agree that this is usually reserved for servitors, daemons, and the criminally insane (and sometimes not even that last one)).
He might also gain the 'clave skill Stealthy.
His witch staff seems like a Force Staff, but you could add an extra dice to the melee damage I guess?
The Black Crown would provide a combined Vampirism/Regenerate skill while worn, by my reading.
Stats wise he's have an average WS and BS, nothing too fancy.
Sg 42 (I may be a little generous here? He is insane!)
Nv 86 (Raging lunatic, will probably ignore a lot)
Autopistol (with laser sight) and a knife, both basic gear.
Mesh armour provides 4 points on every location it is worn on, so assume 4 points on all except head, with the crown providing 2 points (what happens if it is damaged??).
This is just my first pass at fitting him in with the usual power levels of Inquisitor.
I'm not sure if he would get (or even need) any extra psychic powers, but there might be some good chaos ones somewhere to account for the mind control shenanigans.