Crack Is Cheaper: A direct market copy of the first issue is unusually pricey, currently valued at nearly $200. That's much cheaper than, say, Action Comics #1 or Detective Comics #27 (which will cost you hundreds of thousands of dollars, if not millions), but those comics are many decades old, whereas USM #1 is only from 2000.
Spider-Men, the first crossover between Ultimate Marvel and the 616 Universe, actually wasn't conceptualized as a crossover at first. The real purpose was actually meant to introduce the official Earth-616 Miles Morales, who was meant to become a supporting character in Spider-Man's main title but would go on to become an antagonist in the Spider-Men II crossover.
Peter Parker was also meant to be one of the many deaths in Ultimatum. Bendis decided at the last second that he didn't want the character to die yet because he wanted to tell more stories with him. It was during the writing of of the relaunched book, Ultimate Comics Spider-Man, that Bendis would conceptualize Peter's Legacy Hero, Miles Morales.
Word of Saint Paul: After being asked if the comics would show what happened to [the resurrected] Peter Parker and his happy ending with Mary Jane, an editor stated that Ultimate Peter has been dead and gone for a long time, clearly ignoring the most recent plots at the time. This is later proven false, as Peter is shown to not only be alive and well but to have come out of retirement in the final issue of Spider-Men II.
Write Who You Know: Kong's face is visibly similar to that of Bendis. The character, however, is not an Author Avatar, as he's just a minor background character and never breaks the fourth wall.