You aren't allowed to put three Plasma Guns on the servitors. You have to read the Codex section under warriors. You are allowed to add 1 plasma gun to a servitor. So you would probably want to go with Heavy Bolters on the other two.
As far as Psychic powers goes, depends on what you want him for. Since you want him for ranged I'd say you could give him Scourging. Other powers won't really help you. Hammerhand is good for close combat since it will make his strength 6.. but regular armor saves allowed.
Your Inquisitor is obviously just there to hit Deep Striking units, I'd say drop all the other retinue and just put him next to a squad of guns that can shoot REALLY far. If you put him next to a squad of Russes, he can have them take the free shot at the deep strikers.
[EDIT] Also, I almost forgot. Since you're making the inquisitor a Lord, you can have him bring a Land Raider if you wish for an additional 250 points! That might be good. Also, to the above, you would still need to take the Mystics obviously.
But yeah, just use him to hit the Deep Strikers, also, you can just make him an allied elite choice to make him cheaper and still get the Land Raider.
You don't see da eyes of da Daemon, till him come callin' 
