Why does Harmony use the pseudonym "Danesha" at the Flower Club?
As a precaution. After hours of intimate conversation, some of her more determined customers might attempt to look her up outside her workplace.

If she's so cautious about the men she meets at the Flower Club, why does she agree to get into Scott's car?
Even at the ripe young age of 19, Harmony has a fairly keen sense of who is and isn't trying to get in her pants. Clearly Scott isn't. And the fact that he's throwing around $1,500 just to get her non-sexual attention...well, she's intrigued. But naturally she's on full alert the during the whole car ride.

On page 166, Scott tells Harmony that all the major media companies (Viacom, Disney, etc.) lose money on 90% of their investments. Is this true?
Well, Scott's stretching the truth a little. In the media business, you have your few big hits and your few big flops. Nearly everything else lands a shade north or south of breaking even. Usually south.

What's up with Harmony and her aspirin habit?
She explains in Chapter 12 that the head trauma caused by the police car accident has left her with perpetual migraines. As to how she can dry-gulp three chalkly white aspirin at once, I have no clue. That's practically a superpower.

By the middle of the car ride, Scott is ready to shout Harmony's name from the rooftops. Why is he so taken with her?
More than once, Scott compares himself to an artist who's found the perfect model. For the past 36 hours, he's been immersed in his epic hoax idea, but he knew his entire scheme would depend on a finding a frontwoman who's sympathetic, telegenic and painfully authentic. Harmony fits the bill and then some, hence Scott's glee.

It's not until the next chapter that Scott begins to adore Harmony on a more personal level. But like most smitten people, he has a tendency to exaggerate her good qualities.

In their final conversation at the end of the book (p. 459), Harmony admits to Scott that she had a little bit of a crush on him from the moment they met. Why is she so taken with him?
Look at it from her perspective: this tall, charming, mysterious stranger walks into her life, gives her $1,500, and then offers to pull her out of her squalor and into the limelight. He also treats her like the most special woman in the world, and he's not even trying to fuck her. To Harmony, Scott's practically a fairy tale prince, although she cynically keeps waiting for him to show his dark side, which he does in Chapter 20.