1. Does Ellis try to make a point with the repetitiveness and boredom of the book?
Yes, it's the mindset of that particular era. It's meant as satire, a parody on being a young urban professional in the 80s.
2. Why doesnít Patrickís character show any kind of progression? Is it intentional?
He does show progression. Patrick slides further and further into madness, and he gets more and more involved in his own little world. He becomes increasingly more detached from reality as the story goes on.
3. Whatís more important in this story: Patrick or the society he is in?
Both. Patrick represents the society he is part of, and is a direct comment on the state of the world he lives in.
4. Whatís the point of the implausible things in the book? The police must be the stupidest police ever if they canít make any connection between the horrible murders and PatrickÖ
Again, satire, and there's the whole bit you might have overlooked where all of this is merely a product of Patrick's imagination. Littered throughout the novel there are clues that none of this is real and that it's just one lengthy masturbatory power-fantasy of Bateman.
5. Why is that, that only Patrick goes mad? Is yuppie life maddening for the human soul in general, or is Patrick insane by nature? Will his other friends go mad and murder people left and right in this world?
See above, and as an added bonus I'll say this: the yuppies in the novel are all the same character. They represent a mindset, a social phenomenon. They're not supposed to be rounded characters you should sympathize with, they're presented in a very negative light because the novel is a direct attack on that particular lifestyle.
6. Whatís the point of the line in which Patrick says that he just wants to feel loved? Is he completely deprived of human connections? Oh, but he isnít, itís the world around him, whatís so naive and shallow. Is this a flaw in the book, or does Ellis do this intentionally?
7. Why is Ellis reluctant to give us a real story, which takes place in the real world? Is he unable to write on a different level or is this intentional?
It's a satirical take on the yuppie-lifestyle, or the vapid 80s brand-loving mindset... so there is a real story, but I'm affraid you only looked at the novel from the perspective of the plot. It's sort of ironic to hear someone call the novel shallow.