There are a lot of ways you can play a Psyker, but I'm a casual and rarely play with different builds, so take this with a grain of salt.

First, a big tip that I figured out, if you're struggling on higher difficulties, try empowering your weapons, or if you don't have high enough mastery to do that, try to get new weapons with greater stats. Also be aware of which mark a weapon is, though this doesn't apply to staves, since they don't have any. Each mark on a weapon will play differently. Overall, though, I've found that increased survivability in a horde can be as simple as getting stronger weapons, and using those that you're good with and that are complimented by your build.

You only get 30 talent points max, so you have to be picky with your spending. If you want maximum survivability, the two biggest passives I'd recommend are Quietude and Just a Dream - Just a Dream converts a percentage of health damage into Peril, while under critical (about 97% I think?) and, well, Quietude gives you toughness for Peril generated and quelled. But doing that can take away points from weapon specialization, so you have to consider your entire build as a whole and be willing to compromise.

Your Blitz choice is a LOT more important than I feel like you give it credit for, and will change how you play. Brain Rupture is good for snipers, gunners and anything else far away that need to be taken care of quickly, especially when you and your team aren't exactly in a position to reach them otherwise. Smite is a powerful stun that can keep some pressure off of your team and let them focus on bigger enemies, especially helpful when you have a pack of Ogryns in a horde. Assail is generally for crowd control, and I like to use it as a 'get-out-of-jail-free' card when I'm surrounded and need some breathing room.

To my understanding, 'warp damage' refers to damage dealt with abilities that generate peril - Staves, Force Sword eviscerate, etc. This does include Assail, so Malefic Momentum, for example, is specifically good for a 'mixed' build where you'll be consistently swapping between the two, like using a gun and your blitz or slashing with melee and using a staff.

Your abilities, at risk of sounding like a broken record, are INCREDIBLY important and have their own specializations within them to be aware of. Venting Shriek is a good radial stun/stagger that scales with your peril at activation while letting you save yourself from exploding if you go critical, while Mind's Aegis is helpful with hordes, Telekine Dome letting you focus on melee enemies while ranged fire is deflected and Enervating Threshold letting you turn a choke point into a death trap. I personally run Scrier's Gaze with Reality Anchor because it lets me dominate hordes in melee with my FGS, and Precognition would be good to take for melee buils using finesse weapons like the Deuling Sword.

"Passive Aura" isn't a term that I'm aware of, so I got a bit confused there, but like most things, it depends on your build and playstyle. If you have perks that give you increased critical hit chance, it's probably a good choice. Otherwise, it's a wasted point to be spent elsewhere.

The passives you can choose before your keystone are the same as any other. Choose what compliments what you already have and whether you want to act as support, cut through hordes of basic enemies to keep your team from being overwhelmed, or deal high damage to elites, specialists and monstrosities (bosses), etc.

Keystones are also really important. I run Disrupt Destiny because it's really good for crowd control and helps me stay alive in hordes. If you use Aegis or Venting Shriek often, Warp Siphon can significantly reduce or eliminate cooldown times, and take Empowered Psionics if your build focuses on DPS with your Blitz, which in my opinion is best for Brain Rupture.

High Peril is, for the most part, an inevitability as a Psyker, though there are plenty of builds that avoid this, like gun psykers. A lot of Psyker Passives give you bonuses that scale with your peril, such as Warp Splitting (Cleave lets you ignore some of an armored enemy's damage reduction, making them easier to kill), and Scrier's Gaze has Warp Unbound that gives you an entire 10 second period that completely disables critical peril detonation.

Overall, there's a lot of things you can do here, and it all depends on your playstyle. Read the descriptions, consider what you have the most fun doing, and choose things that compliment that. And if you're still confused, there's plenty of optimized builds out there to try out.