I consider a "large" main cast as five or more featured people. My series has a large main cast of six, now seven "main characters".
This is really good advice. I break my characters' interactions into smaller groupings. It's a lot easier, at least in my opinion, to weave together a bunch of short, cut scenes featuring 1 or 2 characters rather than showing the featuring them together ALL THE TIME.
My advise for larger casts is that if your characters don't know where X character is, YOU should. If the character isn't immediately involved in what the rest of the people are doing, we should know that they are off doing XYZ -- and if you can, show us what they're doing. It's helpful for subplots as well as explaining why someone disappeared for X chapters.
I also encourage that if you're going to name a character, they should have a "job" in the story. Sure, it's one thing to name a character if they have dialogue and interact with other characters in a scene. But if Terry the guy from the best friend's gym, has one scene, I'd say you're okay to refer to that character in "general terms" if needed later in the story. I've had trouble keeping characters straight if all there is, is a list of character names.
Cop shows or crime procedurals do an okay job with larger casts. Everyone who is featured regularly has a key role to the story and they don't add in new players without solid reasoning.