There is no correct or incorrect number of attributes on a job's scorecards. The number of attributes included on a job's scorecard depends on your organization and the complexity of the job.
However, please be aware the more attributes included on a scorecard, the more interviews your organization will need to conduct in order to cover them all. With this in mind, Greenhouse Recruiting recommends selecting 6-12 attributes for each scorecard category.
For more information on scorecard best practices, check out the articles listed below: