We currently using Shopify payment integration for our Shopify app fees.
But we need to switch this to our own processing with PP Pro.
... So we need to tie into the app install procedures in Shopify app store, and facilitate recurring payments, and then have some event handlers to check if the app is still installed before processing the recurring payments, and for interrupting service if payment fails.
... First step is to simply replace the existing integration which is using Shopify payments.
2nd step is to create different priceing tiers, depending on traffic and/or product count in the store..But the payment interface has to be built as part of the app install, using the routines like app store requires.