Minor and one-off characters can be really, really effective storytelling tools. They're like extras. They pop in, they provide background colour, etc. Like the boy in Local Hero who flies by on the motorbike every single time MacIntyre steps out the front door. And that's practically his only role, though he pops up in the background in a couple of other scenes which are made considerably more hilarious by his presence.
What you should avoid is relying too much on minor characters. That's true of any storytelling technique, but there are a few different ways minor characters can be overused. I'm guilty of inserting them too often just to get killed--Redshirting--and while it's okay a couple of times once it becomes obvious that they're Redshirts, it's a problem because it saps away story tension. If your story's core is entirely predicated on minor characters you might consider whether your mains are too passive, although even then there are ensemble stories.
You can do the same with a lot of main characters. The Long Patrol is one of my favourite books ever and it's got two main character groups alternating through the plot, one of which contains about 10 characters given mostly equal weight and the other of which contains 4-5 who are all treated as main characters. This happens all the time, though it can vary by genre so read in the genre you're writing in.
The biggest thing here, though, is that you're asking the wrong question. You're looking at this all wrong, as if it's some kind of quota or formula. Write a good story and it will become a good book. There really is no simpler way to put it than that. There isn't some magic number of characters, or words, or plots. There's what you come up with and your skill in saying it. Anything beyond that is immaterial--interesting, often, for the sake of discussion and analysis, and so useful but hardly a guide.