I discovered TVTropes after I had laboriously thrashed out my own potted advice on how to develop parties of PCs for character-focussed RPG campaigns. You can cut to the chase with cast calculus , which will tell you a lot of interesting things about how ensembles are done in TV, film, and literature: and why that way works (in TV, film, and literature). It doesn't all work the same in RPGs. Nevertheless, this is an interesting place to start.
Beware! TVTropes will TVTropes will ruin your life .