Enough that each one has a distinct exit criterion a manager can inspect, and no more — typically five to seven for a B2B software motion. A stage that can't be failed isn't a stage; it's a label. Add a separate renewal funnel rather than stretching one pipeline over both.
Define each stage by what must be true to leave it, then attach the artifact that proves it. Publish what managers inspect at each gate, how and when, and what good looks like — so the design is usable in one-to-ones without redesign. Stage timestamps should be stamped, not derived.
Every claim above comes from work LeanScale published. These are the sources.