It's not the number of characters - it's how you structure the story. Of course, more characters means a larger cast, more scheduling, higher budget, blah blah blah... but in terms of story flow - it's about making the story, or STORIES distinct.
Is it warring 'factions'? Okay, we know the five people on this side, and the five people on that side - so really - it's only two characters - the opposing 'sides' that you're writing about. Each 'team' has a number of players - but the audience understand's that the STORY follows the dynamics of each side. So when a 'player' is on screen - we know who and what their motivations are.
Is it a POV series? Perhaps there is ONE EVENT taking place. A disaster for example. The ship has overturned, the invasion has begun, the building is on fire. Then the story moves from group to group, to show THEIR point of view on how they are dealing with the disaster. THIS team is trying to climb out a window. THIS team is trapped in a stairwell. THIS team is on the rooftop, trying to start the helicopter. Again - the story is CLEAR. Get out of the building - survive the earthquake - whatever. And we are simply jumping from point of view to point of view. The motives are clear.
Is it a VARIATION on a theme? This is handled brilliantly in "Love Actually". There are a series of interlocking stories. Each story examines the THEME of the film, in this case, the nature of Love and Relationships. We see how it works with the Prime Minister and the Clerk, with the Young Boy and his School Girl Crush, the Married Couple and the Affair, the Desperate Single off in the Strange Land, The Best Man's Crush on the Bride... Each relationship is a self contained story. The screenwriter and director deftly weave the stories into a single tapestry, with the barest hint of connections between the characters. This is the most challenging, and most rewarding of the 'multiple character, multiple story' constructs.
There IS economy in time and budget to be had in smaller casts. Sometimes you'll see production companies explicitly looking for "Low budget comedy, no more than five characters, three locations" for example. That's the sort of thing one usually sets out to write with the budget in mind - if YOUR story is a ranging multi-character epic - then write it. If it's good, it'll get some heat.
Write on.