Think about your business partners. Which partners do you want to send documents to electronically? Who do you send the most Invoices or Purchase Orders to? How many of your partners should get their documents in the same format?
Pick as your starting Document Type the one that your biggest business partner or the largest number of your business partners want to receive as EDI. Pick as your file format the one your largest or the largest number of partners want to receive.
Now build and test an EDI Profile with a single EDI Form. As you go, try to replace anything specific to a single Customer or single document or single Document Type with an EDI token. Build your query to generate custom EDI tokens carefully. Think about where it might have problems:
Sales Reps who are not Employees might not have email addresses in the xTuple ERP database
The billing Contact for a Customer might not have an email address, so have a fall-back option such as the correspondence contact
The API Views might not have all of the data you need, so you might have to build more complicated queries using the regular xTuple ERP database tables