I write screenplays with a lot of characters. Can't help it. It's a requirement of the story premise choices I make. I haven't figured out how to write an orphanage, City Hall, golf tournament or tribe of natives with only five characters. I'm sure it can be done and done well, but not by me.
The core of my stories does always involve only one to five primary characters but as yet, I haven't written a story where everyone outside of my circle of "agonists" are extras or prop people. What are prop people? A term I just made up (or maybe I only think I did) for cast members who amount to little more than a prop. Sure, I have some prop people, too, but there are usually several other minor characters who contribute to humor, exposition, etc. They are important.
So we have major characters, minor characters, extras and prop people (non speaking extras). Did I leave out any others?
Seven deadly sins of multiple characters:
(1) reader/audience confusion
(2) unnecessarily long screenplay
(3) spreads story too thin
(4) characters with overlapping purposes
(5) repetitive characteristics
(6) too much dialogue
(7) accidental side streets
Is that all of them? Well, what if you can write multiple characters without doing any of those things?
As a followup to How Good is Good?, I looked at some of my favorite screenplays to figure out just how many characters is too many.
Back to the Future managed a high school, small town, and senior prom while maintaining its focus on about five characters. There are a lot of extras and prop people. See? It CAN be done and done well. But is it the only way or even the best way?
Twelve Angry Men - Obviously, this wouldn't work with fewer than twelve characters and while there is only one primary protagonist, each member of the jury is a necessary part of the story. Are all characters equally weighted in importance? No. How many character conflict combination opportunities is that? I can't do the math. But it works.
Pirates of the Caribbean - This was a big cast with two pirate ships and a navy vessel to staff but the story is about three primary characters. Sure, you could ditch the governor, but why would you want to? And although Norrington & company aren't THE main characters, there wouldn't even be a story if Murtogg and Mullroy didn't pipe up at just the right time because of a chance meeting with Jack Sparrow. Lots of characters AND we even know their names. It works.
A League of Their Own - We know that we need at least nine characters to make a baseball team. The story centers on one player, her sister, and the coach, but not only do we know the names of each of the other seven players, but they each have a storyline to some degree. Shirley can't read. Betty loses her husband. Alice never washes her socks. Mae gets around and Evelyn is the launch for "There's no crying in baseball". It works.
So how many characters is too many? I'm thinking any character that commits one of those deadly sins is one character too many regardless of the number of characters in the story. But, don't take my word for it. This is an amateur hypothesis, not a professional conclusion.