Is it ever explained how Tyler knew all of the "useful information" that he did?
Short answer: there is nothing in the movie which explicitly explains or demonstrates how Tyler Durden is so informed. Presumably it is because the Narrator (Jack), given his insomnia, has a lot of time on his hands to research these things. Little is shown to indicate that Jack would even be aware of anything related to Tyler's knowledge other than soap and human fat which are only mentioned in passing. Both are things he deals with in his job as a recall coordinator: the soap as a traveller staying in hotels, and the human fat is encountered during an insurance claim for a car wreck (the "recall formula" scene).
The narrator always seems to be interested and amazed at all of these facts that Tyler knows.
Long answer: in the opening of the film, the following dialogue occurs which really spells out how Tyler Durden's knowledge and Jack's fascination by it functions in the film:
Narrator: I know this because Tyler knows this.
Tyler: (Looking at the timer on his belt) Two and a half. Think of everything we've accomplished.
Narrator: Suddenly I realize that all of this, the guns, the bomb, the revolution, has got something to do with a girl named Marla Singer.
The "something" is that all things "Tyler" all get back to Jack's inability to relate to and maintain an emotionally intimate relationship with a woman. In particular, a woman with whom he has a lot in common. Why does Jack need to construct an alter-ego which can research "off-limits" topics? Is this a defense mechanism to keep himself safe in a perennially adolescent fantasy world (instead of pursuing a potentially disappointing yet mature romantic relationship?) Yes.
Jack's inability also fits in with his existential angst, ennui, and loneliness in a capitalist and consumer-driven culture from which he feels disconnected (dissociated) and in which he feels trapped. Given his disconnection from the world, he cannot make sense of the things which he is fascinated by and Tyler becomes a convenient fiction for him to explore the world outside of the constraints of his job and the imperatives of consumption and capitalist profit. In this sense, Marla is symbolic of Jack's general disconnection from his own humanity as well as his feelings of adult inadequacy, e.g. the hardships of delayed individuation in a society without rituals for establishing and confirming member status as a valued adult. Note that he says "a girl named..." and not "a woman". The naming of things is also an issue: who does the naming (other people? Corporations?)? It is worth noting that the Narrator's name "Jack" is never explicitly used.
"I know this because Tyler knows this" is a feature of Jack's dissociative identity disorder while the two dialogue. In the opening scene, which is at the end of the movie's timeline, however, Jack has begun to figure out what is going on, so he is also realizing that he is Tyler and thus, whatever Tyler knows, he knows.
Tyler's comment, "Two and a half" while actually referring to the time left before the bombs go off is also an allusion which can be read as the 2.5 characters comprising the relationship between (1) Jack, (2) Marla and Tyler (the 1/2 character). "Everything we've accomplished" is also Tyler telling Jack, "you've accomplished your goal of starting a relationship", i.e. it's time for me to go if you want to find your place in the world and have a chance at making this relationship with Marla succeed. A few moments earlier Jack says:
Narrator: That old saying, how you always hurt the one you love? Well, it works both ways.
"All of this ... has got something to do with a girl named Marla Singer." Jack hurts Marla. Marla hurts Jack. How to break this co-dependent cycle and relate as two mature adults? Likewise, society hurts Jack. Fight Club and the bombing are Jack's way of hurting society. Not such an easy cycle to break, but possibly one ameliorated by maturely accepting yourself as an adult and making peace with your lot in life? Finding a mate can go a long way towards making and maintaining this peace. Conversely, making peace with your life can help a lot to grow a secure and sustainable relationship. "It works both ways."
Narrator: For six months, I couldn't sleep.
...and, without sleeping, he's has a lot of time on his hands. Presumably, he's been researching things which are outside the purview of his corporate and consumer lifestyle. Having this knowledge compartmentalized in the Tyler Durden persona simply helps him to rationalize self-destructive decisions (such as ignoring his doctors advice to lighten up and get a good night's sleep.) Remember, he does get a good night's sleep after an emotional release into Bob's "bitch tits". Instead of seeing he needs a woman in his life and rising to the challenge of improving himself in order to obtain a healthy relationship, Jack rationalizes that he can maintain his status quo of insomnia and "recovery addiction."
What caused his insomnia? The movie shows a Starbuck's coffee cup as he mentions this and we here "couldn't sleep" echo repeatedly. Also, he travels frequently, presumably crossing time zones and suffering jet lag. As Jack's doctor informs him, however, there is nothing "wrong" with him which would be causing insomnia. Given his inability (and/or desire) not to follow his doctor's recommendation to "lighten up" his condition worsens resulting in his dissociative identity disorder. It is worth noting that the condition is a neurosis (and not a psychosis) as he is able to sleep after his emotional release at the support group for survivor's of testicular cancer. While his condition might not be caused by a physical disorder, the "Starbuck's world" which the movie portrays arguably also has something "wrong" with it:
Narrator: When deep space exploration ramps up, it will be the corporations that name everything: the IBM Stellarshpere; the Microsoft Galaxy; Planet Starbucks.
Did something happen six months ago? We don't know. We do see here that Jack suffers from anxiety at the thought of a world where corporations (and their profit motives) "name" everything (instead of humans, like parents naming a child or lover's naming their relationship a marriage). Presumably, however, Jack's mental disorder arises in this six month time period and is exacerbated by being stuck on "Planet Starbucks". The things Tyler reveals to Jack about the world also function as commentary upon the "wrongness" of the "Planet Starbuck's", e.g. that the best (!) soaps can be made from liposuction fats (i.e. the irony of clean and healthy skin recycling the waste of a pursuit of superficial "perfections" only to sell those same undesirable fats back to the beauticians); or, that things as ubiquitous as gasoline and frozen orange juice concentrate can make napalm; or, that it feels "good" to get in a bloody bare knuckle fight; or, that the many ways those in the service industries can exact their revenge, etc.
We can presume that his alter-ego has had plenty of time to research trivia prior to revealing himself to Jack on the airplane. While this "research" might be irrelevant to Jack's work-a-day lifestyle, Tyler is free to explore and obsess over whatever fascinations Jack might otherwise suppress while trapped on "Planet Starbucks". Given the early scene where he describes his own consumerist obsessions (the Ikea furniture in his apartment and "artisanal" foods), obviously he is a tenacious devourer of information.
Narrator: If you wake up in a different time and a different place, could you wake up as a different person?
On one level, that Tyler knows all these things about soap and bomb making which Jack doesn't simply functions to demonstrate what a different person Tyler is. From the outset, the movie encourages us to imagine that Tyler is an actual person and not an alter-ego.
As for the stuff he's so knowledgeable about, only the fat and the soap have any real set-up. Shortly after Tyler passes Jack on the airport walkway, Jack's monologue mentions the "single-serving" shampoo/conditioner combos and tiny soaps available to business traveller's, but that is about it. Shortly after, Jack's work associate mentions the "fat burned to the polyester seat" in a car accident.
Insurance Investigator: The father must have been huge. You see where the fat's burned to the seat? The polyester shirt? Very, "modern art."
As these things get repeated, all of this adds up to setting up the viewer so that they do not question the associations and suspend any disbelief until Tyler's character can be revealed. Given that such things are a part of Jack's work-a-day world, it makes sense that they are there as fodder for Tyler's mischievous investigation. Prior to their meeting on the plane (about 22 minutes into the film) there is nothing else which sets up homemade explosives or other specific aspects of Project Mayhem (other than their function as metaphor for Jack's self-destructive predicament.)
In the film's resolve, Jack is with Marla, presumably having rid himself of the need for an alter-ego replete with all sorts of trivia and plans of conspiratorial mayhem, and, otherwise ready for a mature, adult relationship.