(1) You write that 'the Supreme Court has gotten the verdict it wanted.' Why does the Supreme Court want to convict Sollecito and Knox?

Presumably, because they watch the same TV shows as everyone else in Italy, and are convinced that Sollecito and Knox are bad characters, and are furthermore convinced that the Italian public thinks that Sollecito and Knox are bad characters, thus allowing them to play the role of "heroes" doing their duty and standing up for "justice".

(2) In the room murder was committed, no DNA evidence pertaining to Knox and Sollecito was found. How does the prosecution explain that only one assailant (Guede) left traces of DNA but the two others left no such traces?

Firstly, of course, they claim that the bra clasp DNA counts as a trace left in the room by Sollecito. Secondly, the original lead prosecutor, Giuliano Mignini, at one point speculated that Knox directed the violence from outside the room.

(3) It is said that the evidence shows that Kercher was killed by multiple people. What is your take on this?

It's just plain wrong, and entirely motivated by the desire to imply that Knox and Sollecito were involved. It's possible that Guede had one or more accomplices (of whom no trace has been identified), but parsimony argues against it.

(4) Perhaps most basically, how did Knox and Sollecito get implicated in this crime? I mean there were a lot of witnesses being questioned but how did the police/investigators somehow get the idea that Knox and Sollecito were suspects?

They were convenient, vulnerable (no lawyers, unlike the other housemates), and unaware of the specific way in which the investigators apparently expected all innocent humans to behave in such a situation. In short, easy targets for an impatient, quasi-panicked police force in need of a quick "resolution" to the case.

Well, it's the word I'm using. Here.

When Knox was first convicted of murder, there was outcry in the U.S. that she was wrongfully convicted, based on shoddy evidence. When she was acquitted, there was nearly as much of an outcry in Italy that the courts had succumbed to American pressure.

...

There is a valid extradition agreement between Italy and the U.S., but the U.S. has not set much of a precedence in returning suspects for such matters. Italians point to a number of high-profile cases over the years in which they say American suspects have been accused of wrongdoing and criminal acts, but have been let off lightly.

The way that nationalism enters is that people feel that criticism of the verdict (especially coming from outsiders, as it mainly does in this case) is an attack on the nation's institutions (specifically its justice system), and thus on the nation itself.

In other words, if Knox and Sollecito were innocent, that would be a soldier for foreigners to use against Italy, and thus must be defeated at all costs (Sollecito's nationality notwithstanding).

especially when the other suspect is also a foreigner, and from an ethnic group Italians dislike much more than that of Amanda Knox.

I wouldn't be too sure of that. Italians are not likely to be openly racist, but their distrust and even dislike towards non-EU nationals (or "Extracomunitari") is fairly well-known. Anti-American sentiment is not unknown there either, due in part to the country's legacy as a sort of "soft-power" battlefield during the Cold War period.