Estimate time to write a resume.
Writing a CV is dominated by the first version. Each role takes real time to write properly — finding the actual outcome rather than describing the duties — and formatting is a fixed overhead. Additional tailored versions cost only about a quarter of the base, because the content exists and only emphasis and ordering change. That asymmetry is the argument for building one strong base document rather than writing each application from scratch.
CV production time
Base minutes = roles x minutes each + formatting; each extra version = base x 0.25; total = base + extra versions x that
Three to four hours for a first proper version with five roles. Most of that is not writing but working out what each role actually achieved in measurable terms, which is why it cannot be done in twenty minutes.
One per distinct role type you target, not one per application. Two or three usually covers it, and each application then needs only a light adjustment rather than a new version.
Once, yes. A clean, consistent, machine-readable layout is reused across every version and every application, so the cost is amortised. Redoing it per application is wasted effort.