[@Wraithblade6] All of this coming from the guy in the chaos campaign who's not devoted to chaos...

And, to rebute:
1.) Combat magic is nearly instantaneous. It's like pulling a trigger on a weapon. Another psyker can sense the energy and try to disrupt it, but once it's done it just happens. There would be no point in putting psykers on the field of battle if they couldn't manifest their powers quickly enough to respond to a gun being pointed at them. This applies to all powers equally, regardless of size. The exception is ritual magic, which is explicitly not used in combat for that purpose.
2.) Over the past several hours, he's manifested 5 spells. Yes, psykers are limited. On average, a properly trained librarian can cast two to three spells reliably within the time frame of discharging his bolt pistol in a single burst. He would need to focus himself again, in somewhere around two to three minutes.
The primary limiting factor on what a psyker is capable of is how much warp energy he can control at one time, and how much is on hand. The actual act of manifesting warp powers isn't particularly straining in any physical sense, because none of energy being used comes from them; it all comes from the warp. That of course means that, were we in an area without a great deal of latent warp energy, psykers would be severely hindered. However, we are currently in a place where the warp is literally [b][u]Bleeding into the Materium.[/u][/b] There's plenty of energy on hand, which would give any psyker a sever power boost if they wanted it.
3.) No. Just no. As previously stated, the power manifests instantly. That power in question is a sudden blast of telekinetic energy that would literally detonate immediately between the two of you. No warning, no time to react, no cover to hide behind. And, before you say anything, remember; We are talking about Literal magic. By definition, it doesn't have to follow the laws of physics, let alone adhere to any kind of common sense.
4.) Yes, there exists a chance whenever a psyker manifests a power that it could backlash on him. Such events are uncommon, and experienced psykers rarely have any issue with them. Equally as likely, by contrast, is a phenomena where in the psyker channels too much warp energy, and channels the excess out through his body in the form of sheer power. This gives the psyker the rough equivalent of warp-energy terminator armor.

As for the number of people who play the tabletop game... Well, there's a reason that the company who owns the property is a miniatures company, and not a publisher.
Example: This website has about 72,000 registered users. By comparison, [url=https://www.dakkadakka.com/dakkaforum/forums/list.page]Dakka Dakka[/url]-a website dedicated to Warhammer 40,000, specifically to people who play the game and buy and use the miniatures to do so-has a registered user count of well over 100,000. But, of course, it's not like it makes sense that a website dedicated to people who enjoy narratives and roleplaying has primarily heard of a popular property via its roleplaying games and novels... Oh, wait.
Also-I'm in my twenties, and I live on less than 10k US a year. I watch Bruva Alfabusa too. He's funny, but even he openly admits the 90% of the things he depicts as cannon is nothing but horse-shit that's poking fun at older depictions of the world that no longer apply.

As for handling my character; Well, I'm not the one who opened fire on another PC without any provocation whatsoever, with the only justification being that you're distrustful of xenos because you're an imperial, in a Chaos-controlled RP. If you'd have just asked, I could have told you that would be a Bad idea. And it's not like Urgrugg hasn't just murdered people before for exactly the same thing. Between the two of us, I'm the one who's yet to actually do anything wrong.