Start with the destination
Define where the product will be sold, who will import it and which use case you are claiming. The same physical vehicle may fall into a different regulatory category depending on assisted speed, rated power, throttle behavior and local rules.
Turn requirements into design inputs
Create one living matrix for vehicle classification, battery transport, charging, EMC, mechanical testing, labels, manuals, warranty and after-sales obligations. Give every item an owner and a validation stage.