I’m in some similar situation where I want only to allow user access for generating proposals or invoices and only those. 
I am considering use of Zapier. I already have 4 API’s for QBO, Device Magic and Trello that link actions, filters, triggers to generate proposals and estimates. You could have something as simple as fields in an excel document that trigger estimates and invoices. I’m a dyslexic carpenter and I created a Zapier API that starts estimates whenever a new Trello card is added to a certain column on one of my Trello boards. You should be fine with excel to qbo API creation. 
https://zapier.com/apps/excel/integrations/quickbooks#:~:text=Microsoft%20Excel%20%2B%20QuickBooks%2...).