Eight to ten lines should be sufficient so that if you do mess-up or need to place odd pieces, then you will have room to work with.
He wasn't going to mess up her interview.
Sometimes they mess up and over react, especially when they're scared.
But in the dark, just feeling around for 'em—the stones I'd left—I was scared we might mess up and make a wrong turn.
Besides, it would mess up your nice new uniform.