Nice. Just played around with it and notice line of sight required on librarian armor. However, chaos traitors were not and I nearly lost a captain armor. Thankfully took no losses but it was close and I think if I got slightly unlucky the entire 18 man team would be dead lol. Not enough experience to know how you will balance psi. Good luck tho! The potential is insane, especially when you consider the potential abilities librarians have in the board game that could translate new psi gameplay.
In board game, the librarian has to check to see if he doesn't kill himself basically when using his powers. Maybe you can use combination of bravery, stamina, and morale? Stamina is already there, but how about the lower this combination of stats overall , the higher the chance the librarian will hurt himself and others around him majorly (the warp breaks through his mind) if he tries any special abillity (mind tome, future spells?). Idk about the chapter teaching tomes, think those should just stay bravery and/or stamina.
The idea I guess is that if the librarian is more tired, more chance of ability backfiring. Or if they are not brave enough they can hurt themselves trying powerful spells. Dunno anything about modding so dunno if this is possible. Good luck anyway.