The document here would apply: https://shopify.dev/concepts/about-apis/rate-limits#resource-based-rate-limits
There are rate limitations for other API calls, and the same document describes how they are restricted.
GraphQL Admin queries are limited to a max of 1000 "cost", but this 1) clears out every 20 seconds and 2) applies to apps.
You could potentially adopt a platform such as the one we offer (see yakety.co.uk) and only use Shopify for the transaction itself. This is called "headless" commerce. You could create unlimited variations and still manage your finances through Shopify. If that would be of interest then I would be happy to discuss further, see my signature below for contact details.