Where does Commerce Stripe store the plans that are created on my stripe account?
While I'm not familiar with Stripe, it looks like the commerce_stripe stores the details in the remote Stripe system via the stripe-php library

e.g, in commerce_stripe_submit_form_submit

Stripe_Customer::create
...
Stripe_Customer::retrieve


The other place for payment gateway settings will be on the individual payment method configuration form under Rules.