A: The current set up only uses Gumroad. I can, if you send me an email provide buyers with a Stripe integration, but it's not as easy to use as the Gumroad one.

I'll look into woocommerce. I think you can use OnlySheets with any payment processor that has an API webhook similar to Gumroad Ping. I've done custom integrations for clients that use Shopify and Zapier. But OnlySheets right now is strictly useful for Gumroad.