How many people in a novel?

I find it strange that even - especially? - in a vast novel like War and Peace, in which Tolstoy creates the illusion that he is depicting an entire world - because of the multiple families, the vast historical sweep, the variety of settings, the contrast not only between the two major eponymous themes of the book but also (to a lesser extent) between classes - there is a counterpoint as well. At the same time that we feel that the novel is vastly populated, it also feels tiny and in a way contrived. This sense is heightened almost to the point of the ridiculous in the chapter in which Nikolai Rostov, retreating with his troops toward Moscow, stops at an estate for no obvious reason - to get provisions? - and it just happens to be the estate of the other major family in the novel (Bolkonsky), where he finds Princess Marya in fear and mourning, and he stands up for her against the revolt of the muzhiks (serfs) and escorts her to safety - and obviously a romance is about to bloom. In all of Russia, he rescues the woman whose brother had been engaged to his sister. This makes the novel feel both grand and claustrophobic, contrived. The exact same feelins arise in Proust and in Powell's Dance to the Music of Time (the latter to a literally laughable extent). But as I think about it, life is or can be this way as well, filled with odd coincidences and tiny degrees of separation, and we remark on this all the time. Novelists have to work through this terrain very carefully. The plot must not feel contrived or preposterous, except occasionally for comic effect (e.g., Dickens). But the threads of the story msut be drawn together through interaction of characters, and a novel, even an enormous one, can contain only so many (a counterexample may be The Man Without Qualities, which is constantly introducing new characters, and which I could not finish). How do you cross the characters' lives without resorting to contrivance? What effect do you want, what effect do you achieve? Tolstoy, as you'd expect, achives a virtually perfect balance between a vast world, the illusion of the whole world, through selective representation (cf. Chaucer), and the sense of a tiny, insular society in which the characters live within their limited visions and social sphere, ignorant of the world around them.