Imaginary friends, but friends nonetheless!
Large casts of characters are my friends. It's not rational. I just end up with them, no matter how I try to dwindle the numbers. This is not a bias against small-crew story. It's how my mind works.
There are challenges that come with writing when you have so many characters that influence your story. They have to be easy to remember, and you need to convey their personality as much as you can with the little 'screen' time they get.
Every word matters.
Never miss an opportunity to make your character more distinct. This is always true, but it's even more important with large casts. Give them habits. Make their voices strong. Exaggerate their traits a little, so that they become more obvious. Unless this character is often in scenes, you can't afford to make him bland.
Large casts can get your readers lost, but when handled well, they make your story complex and colourful. I just hope I have the talent to pull it off!