Epics and stories, answered in full.

Price the avoided loss instead of the gain: the fine, the contract at risk, the run cost you stop paying, the hours the migration hands back to the team each month. Use the same currency and the same window as every other epic on the roadmap. If nobody will put a number on it after that conversation, you have learned something about its priority rather than found an exemption. Standing engineering work is different: it belongs in the quarter's Tech Debt epic, which is sized as capacity rather than priced as value.

Precise enough that someone else could re-run it and land in the same order of magnitude, and no more. The point is not accuracy to the pound, it is exposing the assumption: which population, what lift, what one unit is worth. A wrong number with visible arithmetic gets corrected in five minutes at validation. A confident number with nothing behind it cannot be corrected at all, only argued about.

Product writes it and finance checks the conversion. The product manager owns the population and the expected lift, because those come from research and funnel data. Finance owns whether you are converting at revenue or at margin, and whether the window matches how the business reports. Getting that second signature once, at the start of the quarter, avoids the meeting in April where a £1m roadmap turns out to be £300,000 of gross profit.

No. If neither delivers anything alone, they are one epic split for scheduling convenience: merge them, or move the combined work into a single quarter. If one delivers something alone and the other adds to it, price the first at its standalone value and the second at the increment only. Never write the same pound into two tickets.