Hi Frederick,
I just replied to another thread - Parameter user registration - with a write-up showing how you can use Gravity Flow with the user registration add-on to have a single form handle approvals and profile updates. Adding that approach with step(s) related to Stripe should give you a good baseline.
I’m not clear how you relate the WP user to Stripe Customer Portal shortcode, but either using an html field (that is only set to display on the appropriate step in the workflow) or putting it into the instructions for a particular step would be 2 ways to control when/where they see that detail. If you get the workflow setup covering the registration/payment part and run into issues with the portal display, don’t hesitate to drop our awesome support team a message via the support form in your account.
Cheers,
Jamie