I think I finally made a psyker build in Rogue Trader I actually like. I decided to just embrace grand strategist, which I clearly want to play, and create a support heavy character with fellowship and int skills. Idira will be a sniper with some buffing (need to look into bounty hunter and assassin skills to figure out what her focus will be), Argenta will blast heretics as an arch-militant, Abelard will be a vanguard, still deciding on everyone else.
As for what I did, I just went high fellowship, intelligence, and willpower for the sake of commander skills, future grand strategist buffs, and my own psyker stuff. I grabbed pyromancy, which now I have a better understanding of, and will be using to pepper damage on large enemies and help weed out weak ones when I am not able to lightning them away. My psyker powers will start out as my offensive side to my build (I am to also raise toughness a bit, maybe agility, unsure), while I will focus heavily on support skills in archetype.
Picked voidborn for the tasty rerolls and bonuses, yum yum. Does mean I am shit at melee but this is why I have force lightning and make things burn with my brain (that won't be very effective until level 10)