Write down the catalogue and checkout requirements
Specify product count, variants, filters, currencies and languages. Explain whether prices depend on the customer, quantity or location. These details can change the architecture and administration work.
List payment methods, shipping rules, returns and order notifications. Standard platform settings and a bespoke checkout are different scopes; a single payment checkbox cannot describe every business rule.
Integrations and migration can outweigh the storefront
Identify the source of truth for stock, prices and orders. Define how often data synchronises and what happens when a connection fails. Include test cases for partial orders, refunds and out-of-stock products.
For an existing shop, inventory product URLs, customer accounts and order history. Decide which data must move, how redirects are mapped and how the team will verify the migrated catalogue.
Separate launch cost from the cost of selling
The build estimate is not the cost of running a store. Platform plans, apps, payment fees, fulfilment services and support depend on providers and transaction volume.
Use current provider pricing for recurring fees and place those amounts in the first-year planner. Avoid treating a subscription price as a quote for custom implementation.