Notes on Stripe Subscriptions

Set backdate_start_date to current_period_start of the subscription to migrate and billing_cycle_anchor to current_period_end to create a new subscription for the billing cycle you want instead of having to use phases. The invoice would not be creted until current_period_end is reached in the new subscription
Use subscription schedules for migrating prices and products seaminglessly. Remember to set proration behaviour to none to avoid overcharing the user
The migration toolkit for Stripe is not bad if you don't need to adjust usage-based meters
Stripe support chart is really helpful for solving doubts
Use stripe sandbox for testing different scenarios. Unfortunately, users need to be imported manually (or using a script)