Burr is what used to be called a "debunking" biography. The first was Lytton Strachey's Emminent Victorians, that set out to take some heroic figures ( like General Gordon, Matthew Arnold) and show that they had many human defects. Strachey was especially tough on Arnold's efforts to improve the morals of British schoolboys, pushing "muscular Christianity" over science education. Vidal similarly went after the Founding Fathers' unattractive qualities ( and would do it again, in Lincoln). He wasn't exploring new territory as much as busting myths: it was no secret to historians that Jefferson was self-absorbed, Washington was greedy for land, and that both used slaves. But it wasn't quite fair: Jefferson was also quite a gifted political thinker, Washington did also manage to keep an army in the field in two difficult wars and both also did actually have ideals and were inspiring to people around them, and this is somewhat lost in the book. Burr really was genuinely a cynical politician, good at intrigue, quite ambitious, and so often distrusted, even before shooting Hamilton. His conversion of an apparently useful New York water company project into a bank was either fraud or very close to it, and his scheme to try to establish some sort of pre-Texas state in Mexico with an armed expedition was somewhere between foolish and crazy.

Like Strachey, Vidal was gay and so perhaps had greater sensitivity to the moral hypocrisy of the society around him. He was also raised in Washington DC, had close connections to the Kennedys, could see politics up close, and so could easily assume all politicians were cynical. This is likely why he would later conclude that FDR had known about the Pearl Harbor attack beforehand but kept quiet so as to get the US into WWII: there is no real evidence for this, but it was an easy conclusion for Vidal to jump to; that a sitting president would allow a foreign government to bomb and destroy a Navy fleet, kill hundreds if not thousands of servicemen to create an incident to stampede the US populace into war.

I don't know anything about the idea of Van Buren being Burr's son.

There are a lot of possible books on the Founding Fathers and creating the US, but a good readable one that goes from before the Revolution into the early years of the Republic is John Ferling's A Leap into the Dark. There are other good ones on the Booklist including Bernard Bailyn's excellent The Ideological Origins of the American Revolution.