There will be two attacks. On page 190 of the main rulebook, under the Full Auto Burst heading, it says that if you have two pistols in your hands you may fire them both. Page 197 discusses two-weapon fighting, and while it doesn't explicitly say that you make two attacks, note that two-weapon fighting with a melee weapon and a pistol does call for resolving each attack separately. Also, there's no stated bonus for using two weapons other than the potential for two attacks, which strongly indicates that you get to make two attacks -- otherwise, you'd never do it.
As a sidenote, also per page 197, you may only lay down one area of suppressive fire even with two full automatic weapons.
According to the core rules (and I checked for errata), a psyker "...makes a Power Roll by rolling a number of dice up to their Psy Rating (typically 1-6) and adding their Willpower Bonus."
The important phrase here is "up to"; just because a psyker has a psy rating of 4, that doesn't mean they have to (or should) be rolling 4d10 for every psychic power they try to use.
(Note that there was errata that you always have to roll one die, which you wouldn't want to do if, for example, your WP bonus was greater than the Threshold of the power you wanted to use.)
It's also worth noting that rolling 9s isn't a guaranteed path to INSTANT TPK - it just invokes Psychic Phenomena, which CAN result in Perils Of The Warp, and THAT's when things get Bad. (It's also worth noting that results of Psychic Phenomena or Perils Of The Warp do not cancel the effect of the power, unless otherwise stated; you've still rolled a 9, and stuff gets weird, but you also got a pretty good result on that die!)
Finally, the "Favored By The Warp" talent allows psykers to roll twice and choose the better result on all Psychic Phenomena tests; if a psyker opts to enter the Scholar line of ranks beginning at 2,000 XP, he can pick it up at Scholar Arcanum (6,000 XP) for 200 XP. If he opts for the Savant tree instead, he cannot acquire it until late enough that Ascension advancement rules kick in; if your Psyker is still coming close to blowing up everything but has opted to become a Savant, consider letting him take "Favored By The Warp" as an Elite Advance after 6,000 XP.
There appears to be a reference which can answer your question in the Mediafire folder here. It's the file called "Skills with Errata 5c.pdf" (direct link).
It lists what skills each class gets and when in tabular form, so it should be easy to tell which skills have only a single entry.