You will get all the features you need.
I already provide a standardized full-featured payment modules implementation service, and I wish to provide a similar standardized full-featured service for accountancy packages integrations with Magento 2.
I propose you to list all the the features you need, and I will implement them all.
We can include these features and other terms in an Upwork contract (see my Upwork profile) or in a PayPal invoice.