I think something that becomes painfully obvious when you've decided to keep track of all the characters is the nearly absurd number of them (I count 38 significant characters on my list, and this is only the second assigned reading). Yet as the story progresses, what seemed like barely related fragments of various narratives start to coalesce to form the pieces of a classic story. This chaotic mess doesn't offer any easy answers, but if you look for long enough you begin to notice patterns. The book for instance, primarily takes place in Massachusetts and revolves mostly around the Incadenza family. Next you get little bits of plot: the Québecois separatism keeps coming back as well as the life (and death) of Dr. Incadenza. And as if to taunt the readers, DFW tosses in a connection between these to central plot elements on page 137 when Orin calls Hal and asks "What do you know about Separatism?"
Having so many characters also makes make want to classify or categorize them. The best distinction I could think of was between the characters that were central to the plot ('s development) and those sorts of fleeting characters, which I feel DFW uses to illustrate an idea. Good examples of plot-based characters are Hal and Steeply (and maybe Marathe), while good examples of idea-based characters are Erdedy and Schtitt (and maybe Marathe {again}).

Unrelated to analysis; how Dr. I died --> (p.142) (seems really unlikely)
My question about what ONAN stands for answered --> (p.151) (I guess that makes Québecois separatism a little bit more understandable)