How to create a customer in omnipay-stripe
Omnipay has no support for customers. Stripe does have but that part of the Stripe-API is only used in Omnipay to more or less well provide the Omnipay token billing functionality (you can see some bugs in the tracker, for example https://github.com/thephpleague/omnipay-stripe/issues/8).
So asking about how to use omnipay-stripe for customer management sounds more like asking for trouble to me. I would suggest you use the non-Omnipay stripe API to manage your customer handling and keep Omnipay for the payment only.