Sharing Private Documents

Hi, I have looked through the community and the content and can’t find a clear answer to this

We create Master documents that we share with a number of businesses (DocMaker)
Each business will work through the documents to complete them and answer the questions we ask (Editors)
Each business will have a number of team members that will collaborate to complete the document. They wont ever edit the master doc - they will fill in the data in the tables.
The information each business submits is confidential - so each business should be able to see the content/replies from their business only.
What is the best way to do this?

Do I set up a Workspace or Folder for each business and copy the master doc to each folder?
Is there a way to API/Zap the list of team members into each team?
We use and love Google so happy to use Contacts and Google Groups

We already have full control of our user community through our platform - grouped into businesses - so if we embed master document into each business space we can control access/security. If we embed we have a business code for each business and this can be a dynamic filter making sure that all the CRUD operations that happen in each form apply only to the data in that business but only if we can apply a runtime filter with a parameter passed to Coda containing that business id.
It seems like the embed option is the best one - where we control the access rights for each business - then we have to make sure we can pass the business ID to coda on request at run time.
Any comments/idea appreciated!