You can have up to 20 Salesforce dashboard components on a dashboard but that doesn’t mean you should.
As a best practice, keep Salesforce dashboards organized by category. For example, have all sales-related dashboard components on one dashboard and have all support-related ones on another.
This may not seem necessary when you first start using Salesforce but over time your users will want more and more dashboards.
If you don’t follow this simple plan then eventually it will become difficult for your users to find the dashboards they want and you will be accused of creating dashboard madness, or even worse: decreasing user adoption.