In Proforms you have 2 Authorize.net attribute "sims" and "arb". If I'm not mistaken, the ARB one is an on-site payment method, just like Stripe. That would be a good place to start to build a Stripe one. The code is in models\attribute\types\payment_authorize_arb.
I would then suggest you grab the code From Community Store Stripe plugin to see how to adapt it. You'll have the choice between the inline form which is a custom form you can make to your liking; or Stripe's own popup form which is easier to implement but less flexible.