Five: funnel and conversion by stage, pipeline creation against plan, forecast and coverage, activity and speed-to-lead, and data hygiene. Anything beyond those five should exist because a named person makes a recurring decision with it.
Build them as part of the system, not after it — dashboards specified during the build force the data model to support the questions. The hygiene dashboard is the one most often skipped and the one that keeps the other four honest.
Every claim above comes from work LeanScale published. These are the sources.