Which steps should not be automated?
Put a human approval gate in front of anything irreversible - releasing payment, sending to an outside party, committing a contract. The value of automation is not in removing the judgement but in removing the preparation before it.
How should failure be handled?
Every flow is designed together with failure alerts, retries and a manual recovery procedure. Automation that fails silently is more dangerous than doing the work by hand.
How do you prove the effect?
Measure per-item handling time before the engagement and measure it again the same way after go-live. Estimates are replaced by measured figures in what we publish.