Warning - Here Be Spoilers.
I've been devoting a lot of brainpower to ensemble casts in fantasy. I want a new project while I hammer out the fine details of the Sir Albric project. I keep finding myself stumbling on coming up with enough characters that hold my interest. So I keep thinking about ensemble casts, what makes them work, what makes them tick.
Certainly fantasy literature loves ensemble casts. There's plenty of lone heroes and tightly knit groups its true, but when we talk of fantasy, they don't seem to be what comes to mind first. Or at least they don't come to my mind first. Even when you're avoiding the Epics with their casts of thousand, there's still an urge to really inflate the cast.
So I started thinking about Lord of the Rings and the questing party. Lord of the Rings is epic in scope and does have a fairly big cast, but really it comes down to the nine dudes in the Fellowship. Which is a pretty big number anyway. How do you give equal page time to nine characters if they're all in the same spot? Obviously the Fellowship breaks up quick enough that this never really arises. What you really get is a bunch of smaller groups. Prior to formation, the hobbits are a group by themselves for a bit, then there's also the hobbits and Aragorn. After the break-up you get Frodo & Sam, Merry & Pippin, and Aragorn, Legolas & Gimli. Deliberately or not, Tolkien basically breaks them down into the original units, with the newcomers off doing their own thing. ALG go off and have warlike adventures; F&S have their quest; M&P act as the readers' eyes, while at the same time showing the heroism of the underestimated and innocent.
You kind of have a similar model in Eddings' Belgariad. There you get a core group, those who leave Faldor's farm; Garion, Durnik, Belgarath and Polgara. With the addition of Silk and Ce'Nedra, those are the characters that start and finish the book and when you see the party broken up, three of the four will generally be in the same activity group. Barak, Hettar and Mandorallen sort of form their own martial group equivalent to ALG (although Barak also has the buddy act going on with Silk equivalent to L&G, although its obviously a Leiber homage). To a certain extent, Eddings repeats the model in the Elenium. Sparhawk, Sephrenia, Kurik and Kalten are the core group. Tynian & Ulath get the buddy act - which so far seems to be placed outside the core (not that there aren't double acts in the core).
In Feist's Silverthorn, the questing group originally comprises of Arutha, Gardan, Laurie and Martin (although that's never seen on page), quickly joined by Jimmy & Locky (our buddy act), then there's Roald and Baru on the road. Once again, the main role for late comers seems to be muscle, although the original party is hardly short of it (much like Eddings' Elenium crew). The Sword of Shannara is similar to the Belgariad and LotR from memory; a core group of innocents and wizard (Flick, Shea, Allanon), the quick addition of the guide (Menion), then a bit later on all the muscle (Balinor, Hendel, Durin and Dayel).
Lets look at something a bit more modern. In The First Law, Abercrombie mixes up the order a bit. We start with the wizard and a member of team muscle (Bayaz and Ninefingers) and they end up picking up the bildungsroman 'hero' Jezal and the guide Brother Longfoot. There is some additional muscle in the form of Ferro, with whom Ninefingers forms a double act. If you count the apprentice Malacus Quai as another 'innocent', you do have something looking a lot like the traditional questing party, even if its formation has been somewhat twisted round, just like poor old 'Malacus'.
Of course not everything works this way. Take Jen Williams' The Ninth Rain and MD Presley's The Woven Ring, to pick two modern 'quest' fantasies; both of them have parties with only three members, none of them particularly innocent. In the Dresden Files, Jim Butcher has a rotating cast around Harry for when its quest time, although I can't think of anything much in the trad fantasy field with this sort of episodic nature. Going back to Abercrombie, Best Served Cold features a questing ensemble, but there's no real core group or innocents, unless we call Monza and Shivers the core with Shivers being the innocent. Which kind of works.
Nevertheless, it does seem a common enough model: a core group of adventurers, containing the story's innocents and their main guides (or with them joining shortly after), with further characters added as needed, mainly to act as protection. The protection usually forms its own bonds and has its own adventures. If the party breaks up, it usually breaks up into the groups it was originally made up of prior to the formation.
What does this mean? I've no idea. I'm not sure its helped me form new ideas. Although I guess you could have some fun with a story about a core group of protection who stumble across some innocents and their mentor fleeing from danger, take them on, and then find out they're not as innocent as they seem.
But its nice to look at how things work (or at least I think so, and since you've got this far, you probably agree). And the more we think, the more ideas come. I guess the next thing to think about would be just how this effects the dynamics.