The split that tends to hold up is that you own the meter and rent everything downstream of it. Payments, invoices, proration, tax and dunning are solved problems, and building them is pure cost with no upside. Usage metering is the part nobody can hand you off the shelf, because only your system knows what counts as a billable event, when it's final, and what happens on a retry. Build that as an append-only event log with an idempotency key per billable action and aggregate from the log, rather than incrementing a counter on a customer row. The first time someone disputes a usage invoice, and on API or storage pricing they will, you need to replay exactly what you charged for, and a counter can't tell you. The other thing worth getting right early is keeping entitlements separate from price. If plan limits live next to pricing logic in the app, every pricing experiment turns into a deploy. Are you on pure usage, or a base plan with overage?