Sir Arun wrote:I want to include an Inquisitorial Detachment (containing an Inquisitor aboard a Chimera with 3 plasma cannon servitors and some other goodies) as well as an Officio Assassinorum detachment for my Grey Knight primary detachment. Is both possible at the same time?
And if yes, the Officio Assassinorum detachment only has place for 1 Assassin, if I am reading this correct. So is the formation that includes all 4 the only way to get more than 1 Assassin?
You can take as many of any type of detachment as you want. The only restriction is that whatever Faction your Warlord is chosen from, cannot take any Allied Detachments (clarification, the Detachment actually titled "Allied Detachment", they can still ally with themselves as long as they're not using that specific Detachment)
So yes, if the Assassins are no longer "Unique" you could take as many of each as you like, it's just that each one would be its own detachment unless you take all four in which case those four would be a single Detachment. And there is no rule in the books preventing you from allying with as many factions as you like. (GoonBandito is correct that often tournaments or local gaming scenes will often have house rules to limit things they believe to be broken)
For your Inquisitorial Detachment I have a couple suggestions.
You may want to add two Jokaero Weaponsmiths, as they buff the rest of the unit, and they have (I believe) 3 different guns they can shoot (Melta, Lascannon, Heavy Flamer
IIRC). You could potentially have your 3 Plasmas and 2 Lascannons all firing at 48".
You need an Inquisitor to stay with them so the Servitors don't lock down. My suggestion is Coteaz, because of his I've Been Expecting You special rule. I don't think he can take Servo Skulls, so for those you can take any generic Inquisitor you want. My favorite is the Ordo-Malleus in Terminator Armor and a Psycannon.