I did hit, in one of the earlier ones, the question of getting the group together. But that's not even half of it. . . .
Why are they adventuring at all? All the more in the RPG tends to throw out adventure hooks. A wizard, for instance, would be more likely to be on an active quest to obtain new magics. Greed has its place as a motivator, but in a novel you actually have to delineate that, not take it for granted. Also, if all they are is pure greed, they are not well orchestrated.
Clerics, druids, and paladins raise serious questions about why they would be allowed to go on a journey for greed; donations and level-grinding (so as to be more useful) need to be more explicit. Missions would be even better.
Indeed, they all need to be more explicit. A DM can let the players not worry about their motives as long as they are happy with their characters. And if the players want more motives, the players can give them.
Then they hook up -- and it takes a real genius to pull off "You All Meet At An Inn" unless you throw in "And Woke Up in Jail the Next Morning," and make the adventure their sentence (and even then you have to be clear why they don't bolt). A cleric/druid/paladin could be sent on a mission, but why would a rogue or a fight join them?
But having done so, what about adding characters or removing them? Those, of course, must be driven by the needs of the plot. But if two characters died, the party is not going to happen on two characters in the next inn, and after ignoring everyone in every inn thus far, suddenly decide that these two MUST join their party. Worse if they meet in the middle of the adventure, where you would expect mistrust.